Fix displayed information for contracts upgraded from v1 to v2

[patitonar]

This PR fixes the issues mentioned on https://github.com/poanetwork/poa-bridge-contracts/issues/137#issuecomment-461578462

• Display correctly the statistics section, including transactions from before and after contracts upgrade to v2.
• Display correctly list of validators. Refactored how validator list was built. Now it process all ValidatorAdded and ValidatorRemoved in all its variations from contract version 1, version 2 and also when using Rewardable validators contract.

[netlify[bot]]

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[coveralls]

Pull Request Test Coverage Report for Build 466

• 23 of 56 (41.07%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+1.9%) to 6.848%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/stores/ForeignStore.js	0	1	0.0%
src/stores/utils/contract.js	23	37	62.16%
src/stores/HomeStore.js	0	18	0.0%
<!--	Total:	23	56	41.07%	-->

Files with Coverage Reduction	New Missed Lines	%
src/stores/HomeStore.js	1	0.0%
<!--	Total:	1		-->

Totals
Change from base Build 446:	1.9%
Covered Lines:	96
Relevant Lines:	1393

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💛 - Coveralls

[patitonar]

I made some improvements on the solution:

• Now we only make one request to get all statistics of transfers including the one made from v1 version. To get all events and parse them correctly by web3 I use a combination of the bridge contract ABI and an ABI including old events names. This was implemented here https://github.com/poanetwork/bridge-ui/pull/184/commits/954b59d02c0680c156f10da3f835bddb7a08e74f
• Now only one request is made to get all validators list. I tried using a similar approach as statistics and merge all the differents ABIs (BridgeValidators, BridgeValidtorsV1 and RewardableValidators) but the problem was that web3 wasn't able to correctly parse events from BridgeValidators and BridgeValidtorsV1 because they have the same topic but v1 parameter is not indexed so returned data of event was different. So the solution was to build the contract with an empty ABI, get all events and parse them manually. In this way, with one request we can process the events and build the list even if they were generated as part of V1 contracts, V2 or by RewardableValidators. This was made here https://github.com/poanetwork/bridge-ui/pull/184/commits/6616bd74773a3b5cad34500cf33acdd33eae53af

In both solutions deployedAtBlock is used as fromBlock parameter to get the events

[akolotov]

I made some improvements on the solution:

@patitonar thanks. Sorry that I did not notice your initial responses earlier. Now I provided my comments. It could affect your recent changes. Let's discuss this in Slack if it necessary.