Sidetree Node.js implementation

The Node.js implementation of a blockchain-agnostic Sidetree Node using TypeScript.

See the protocol document for the full Sidetree protocol specification.

See the implementation document for the detailed description of this implementation.

Contribution Guidelines:

1. Must pass npm run test.
2. Must pass npm run lint.
3. Must and only prefix the name of a "data structure interface" (interface that is without methods and act purely as data holders) with an I.
4. Must and only export a class as a default export if the class name matches the file name.
5. Must sort imports.