Merge branch 'caching-fixes' into 'master'

Caching fixes

This PR fixes some caching bugs:

* Cached methods have been called locally inside of `CouchDBDao`. The caching proxy was bypassed in these cases. All public methods (even those not involved in caching) are now called on the proxy instance. The here provided implementation is not optimal since it goes against SoC but can serve as a temporary fix. A better solution might involve AspectJ's weaving.

* A wrong key for cache eviction has been used for `NewAnswerEvent` in `CacheBuster`.

See merge request !2