Contracts refactoring

[arminvoid]

@0xAshish reported that making changes in contracts exceeds the max permissible bytecode size of a contract. FYI the byte limit for contract size is 24576. See this.

Moreover, there are a lot of calls among the contracts; interfaces for which are not every clean - for instance rootchain.setWethToken calling withdrawManager.setWethToken AND depositManager.setWethToken - This is code duplication which is one the reasons for large contract sizes. Also, the contracts are abundant with calls of the nature setContract (setExitNFTContract, setDepositManager etc)

To combat the same, some sort of contracts refactoring is required.

[arminvoid]

Proposed solution (discussed with @0xAshish):
Have a Registry contract that acts as the source of truth for all contract addresses. The contracts would get the contract address from the registry. e.g. registry.getWethTokenAddress(). If and when required, the contracts addresses can be changed in the registry. This registry can be acl-ed on onlyOwner in the beginning and a governance mechanism can be plugged in later. The contracts would expose clean interfaces for doing just one thing like createDepositBlock, submitBlock etc. If a contract is getting too big, it can be broken down within itself using the proxy pattern (also for upgradeability), the interface that it exposes will remain the same.