Decouples app setup from running the server

This release decouples setting up express apps to serve metadata-transformer endpoints from actually running the server.

This makes it possible to import metadata-transformer as a library and use it to add functionality to an existing express.js app.

This also removes the requirements for environment variables to be defined in order to successfully use metadata-transformer. Even the web3 client is now injected into the predefined blockchain-based transformers.

Minimum viable Metadata Transformer

This release defines a minimally functional Metadata Transformer which will be used as a topic for discussion/debate in building the production-grade version.

We expect a number of changes until we reach v0.1.0 which will signify that the Metadata Transformer is ready for production use.