refs https://github.com/TryGhost/DevOps/issues/45
- this moves the bulk of the tsconfig file to the `ghost/` folder and
simply extends this file in each of the TS lib packages we currently
have
- this makes it a lot easier to make single changes to our TS config
This is the first pass at an abstract class for our in-memory repository
implementations. It's based off of the existing implementations and
should speed up local development and deduplicate code
