Adds basics for simplifiers
+ MissingObjectTripleNodeSimplifier
+ MissingSubjectTripleNodeSimplifier
+ SentenceTreeSimplifierFactory
Fix @covers annotations
+ support of other data types to MissingSubjectTripleNodeSimplifier
Adds WikibaseEntityProvider

Tests are more like unit tests
Merge pull request #4 from ProjetPP/query

Allows to find the missing subjects or objects