Missing part of dj

[hackfisher]

1. Listening on the events on ethereum and start relay. (Testing on ropsten)

UnsignedTransaction. TX pool (pre validation), similar to order

2. Benchmark, 100K / days? Need 100 days? Cache, optimize.

3. dj relay

• Event: cross-chain transfer event on Ethereum, trigger: new relay push event to a queue.
• Event: New round on Darwinia Relayer Game, trigger:game proposal
• Event: New block confirm on Darwinia Relay, trigger: check receipt (with receipt proof from shadow), call backing module dispatch call according to ethereum event type.
• Event: New block pending, trigger: guard call

[hackfisher]

https://thegraph.com/

[hackfisher]

1 is resolve in https://github.com/darwinia-network/darwinia-common/pull/259

2 is fixed by using SSD, need to to benchmark between different db(Sqlite vs PostgreSQL)

3 is duplicated with #64