Refactor Staking contract (met dragons - eip170)

[tjcloa]

• Optimized modular system introduced
• Staking contract refactored - split into modules
• Tests updated to the new modular structure
• Refactored stakeBySchedule
• Restored function Staking.stakeWithApproval Note: original Staking contract and all the inherited ones are left for review/comparison at the moment and will be removed except for IStaking which is adapted to the new structure
• Restored require/revert messages to their full text
• Fixed governance Team Vesting cancelling out of gas issue [MERGE FORM ANOTHER BRANCH PENDING]
• Fixed issue with CI caused by one of packages

[tjcloa]

Looks good! The modules make sense, documentation is clear. There are only a few things I noticed.

* The stakeBySchedule function was not refactored as expected (details in comment). I recommend refactoring this in a separate PR.

* The error messages were shortened to error codes in the past due to the contract size issue. i would prefer for them to be restored to their full length, because it makes debugging a lot easier.

All done