Proposal to refactor contracts folder for devUX

[tmsdkeys]

The contracts folder is starting to look messy with a large amount of files. External developers will also add the contracts to their projects when downloading npm package.

I propose to clean it up by introducing some folders; i.e. interfaces, utils, examples, libs and core for the main logic.

Example:

.
contracts
├── core
│   ├── Dispatcher.sol
│   ├── OpConsensusStateManager.sol
│   ├── OpProofVerifier.sol
│   └── UniversalChannelHandler.sol
├── examples
│   ├── Earth.sol
│   ├── GeneralMiddleware.sol
│   └── Mars.sol
├── interfaces
│   ├── ConsensusStateManager.sol
│   ├── IbcDispatcher.sol
│   ├── IbcMiddleware.sol
│   ├── IbcReceiver.sol
│   └── ProofVerifier.sol
├── libs
│   └── Ibc.sol
└── utils
    ├── DummyConsensusStateManager.sol
    ├── DummyProofVerifier.sol
    └── GasAudit.sol

External dApp devs would then mostly be interested in interfaces and demo folders.

[tmsdkeys]

Updated this to match contracts prior to public testnet