More fixes and improvements

Improvements:
* semantic queries are stored now, so they have not to be rebuild
  on subsequent calls to searchTitle and searchText
* preparing the fallback search engine and searching it have been
  extracted into a private method
* some more getters to facilitate testing

Fixes:
* offset is reset to 0 before querying for total count to avoid a
  notice thrown by the SQL3 store
* searchText ill not search the fallback engine for semantic
  queries anymore
* the fallback engine was not prepared correctly (e.g. offset not
  set) before searching it, so no matter the offset it always
  returned the first results
* a number of methods were inserted that need to be present and
  forward their params to the fallback engine