Feat/impl serpentor

[storming0x]

Change Log:

• implement SerpentorBravo using GovernorBravo as reference

• Refactors timelock calldata args to struct

• [x] propose (check vote weight at block number)

• [x] queue

• [x] queueOrRevertInternal

• [x] execute

• [x] cancel

• [x] getActions

• [x] getReceipt

• [x] castVote

• [x] castVoteWithReason

• [x] castVoteBySig

• [x] castVoteInternal

• [x] isWhitelisted

• [x] _setVotingDelay

• [x] _setVotingPeriod

• [x] _setProposalThreshold

• [x] _setWhitelistAccountExpiration

• [x] _setWhitelistGuardian

• [x] _setPendingAdmin

• [x] _acceptAdmin

• [x] getChainIdInternal

TODO:

1. add voting weight check for proposals and cleanup
2. add unit tests