[Registry] Add events to contracts

[KilianKae]

• Improve Gas Efficiency
• Improve JS Library by listening for events
• Copy https://github.com/uport-project/ethr-did-registry/blob/develop/contracts/EthereumDIDRegistry.sol
• This would only save costs of creating contract, since all information could be stored in the registry, but event blocknumber would have to be stored on each update
• Further info about events: https://media.consensys.net/technical-introduction-to-events-and-logs-in-ethereum-a074d65dd61e

[KilianKae]

·-----------------------------------------|----------------------------|-------------|----------------------------·
|  Solc version: 0.5.16+commit.9c3226ce   ·  Optimizer enabled: false  ·  Runs: 200  ·  Block limit: 6718946 gas  │
··········································|····························|·············|·····························
|  Methods                                ·               194 gwei/gas               ·       290.00 eur/eth       │
·····················|····················|··············|·············|·············|·············|···············
|  Contract          ·  Method            ·  Min         ·  Max        ·  Avg        ·  # calls    ·  eur (avg)   │
·····················|····················|··············|·············|·············|·············|···············
|  Migrations        ·  setCompleted      ·           -  ·          -  ·      27338  ·          5  ·        1.54  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  addAttribute      ·           -  ·          -  ·      87274  ·          3  ·        4.91  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  addChain          ·       49965  ·      64965  ·      59965  ·          3  ·        3.37  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  remove            ·           -  ·          -  ·      23408  ·          2  ·        1.32  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  setDomain         ·       43994  ·      44150  ·      44046  ·          3  ·        2.48  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  setExpiry         ·           -  ·          -  ·      43312  ·          2  ·        2.44  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDID            ·  setSignature      ·       29917  ·      43988  ·      36953  ·          4  ·        2.08  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDEVRegistry  ·  addAttribute      ·           -  ·          -  ·      33876  ·          2  ·        1.91  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDEVRegistry  ·  addChain          ·           -  ·          -  ·      32187  ·          2  ·        1.81  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDEVRegistry  ·  remove            ·           -  ·          -  ·      13611  ·          1  ·        0.77  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDEVRegistry  ·  setExpiry         ·           -  ·          -  ·      46118  ·          2  ·        2.59  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDEVRegistry  ·  setSignature      ·           -  ·          -  ·      32258  ·          2  ·        1.81  │
·····················|····················|··············|·············|·············|·············|···············
|  TLSDIDRegistry    ·  registerContract  ·       23542  ·      86259  ·      61906  ·          7  ·        3.48  │
·--------------------|--------------------|--------------|-------------|-------------|-------------|--------------·

   Deploying 'TLSDIDEVRegistry'
   ----------------------------
   > transaction hash:    0x9b9c8ed301ec10a634ecc9bd24f1b5ce4c8b223fd20df9c2b328dcfa590c2c50
   > Blocks: 0            Seconds: 0
   > contract address:    0xBc03e14246aeBBBc77FfceE843D25E57078E8249
   > block number:        7
   > block timestamp:     1615476611
   > account:             0x4eB43c1903Bc03375e71B7B159776a5b14103b81
   > balance:             99.946817
   > gas used:            793469 (0xc1b7d)
   > gas price:           20 gwei
   > value sent:          0 ETH
   > total cost:          0.01586938 ETH

   > Saving migration to chain.
   > Saving artifacts
   -------------------------------------
   > Total cost:          0.01586938 ETH

   Deploying 'TLSDIDRegistry'
   --------------------------
   > transaction hash:    0xe3c26497d0c60eaca5936ebde76fdbe7fa8d4e175253a9992d7108819ef2e5a9
   > Blocks: 0            Seconds: 0
   > contract address:    0x2B14C9e44FB27A411D797be558A7aA28Fa29DdEa
   > block number:        5
   > block timestamp:     1615459103
   > account:             0x4eB43c1903Bc03375e71B7B159776a5b14103b81
   > balance:             99.96361754
   > gas used:            357952 (0x57640)
   > gas price:           20 gwei
   > value sent:          0 ETH
   > total cost:          0.00715904 ETH

   Deploying 'TLSDID'
   ------------------
   > transaction hash:    0x985e7433fb2ebf4baa7a05d47e4641271a2b2ec5799f2817e97e1682fae89371
   > Blocks: 0            Seconds: 0
   > contract address:    0x9467490D35D48C9094AcFB5DA2fB4ef1BE66da56
   > block number:        3
   > block timestamp:     1615459103
   > account:             0x4eB43c1903Bc03375e71B7B159776a5b14103b81
   > balance:             99.97132334
   > gas used:            1199552 (0x124dc0)
   > gas price:           20 gwei
   > value sent:          0 ETH
   > total cost:          0.02399104 ETH

Not Event Driven TLS-DID creation, examplary set of each value and deletion:
   93 gwei * (1199552 + 87274 + 59095 + 23408 + 44046 + 43312 + 36953 + 61906) = 144665778 gwei (11.03.2021) -> 290 Eur

Event Driven TLS-DID creation, examplary set of each value and deletion:
   93 gwei * (33876 + 32187 + 13611 + 46118 + 32258) = 14698650 gwei (11.03.2021) -> 22 Eur