…te implementation

- change scrobbler behaviour to remove sucessfully scrobbled tracks from the cache
- change return value of Scrobble methods - will always be either Successful, Cached. Actual failure reason may be stored by Scrobbler cache impl
- Remove CacheEnabled property from IScrobbler. Just use new MemoryScrobbler class if needed
- Remove Scrobbler class, add MemoryScrobbler. No migration path because the behaviour is different - and the old behaviour not that useful

…ScrobbleAsync.ScrobbleResponse not being set

- Update tests data

… tidying