We need to inject the API/SpecialPage endpoint(s) that our repositories are supposed to use for reading and writing into our app.
For now, it should be enough to only create and inject configuration for the Special:EntityData reading endpoint.
Optionally: Think about whether we really want to use Special:EntityData or if we do not need to use wbgetentities any, because we also need language fallback for labels?
- add interface for config object (only tangentially related)
- [add WbRepo interface and prepare tests](https://gerrit.wikimedia.org/r/524513)
- pass and initialize services