These two services are the last constructor parameters of the `WikibaseRepo` class, and they have to be moved to services together, because the Settings contain the name of the default entity source; if we move one but the other, then some tests will start to get confused.
#patch-for-review:
- prepare `EntityHandlerTestCase`
- make some methods abstract and override them everywhere
- [WikibaseLexeme: override](https://gerrit.wikimedia.org/r/648305)
- [WikibaseCirrusSearch: override](https://gerrit.wikimedia.org/r/648306)
- [WikibaseLexemeCirrusSearch: override](https://gerrit.wikimedia.org/r/648307)
- [Wikibase: make abstract](https://gerrit.wikimedia.org/r/648308)
- [Wikibase: don’t hard-code item+property](https://gerrit.wikimedia.org/r/649373)
- [Wikibase: move to services](https://gerrit.wikimedia.org/r/648309)
- update calls to now-static methods / inject services properly
- `getEntitySourceDefinitions()`
- TBD
- `getSettings()`
- TBD