642 add all sentences view

Shall solve #642 by allowing to switch between a view which only displays the sentences which are defined by the ontology we are currently viewing (default, and it is the same as we had before), and a view which displays all sentences.

All sentences are defined as the union of self-defined sentences and the sentences which are defined
by all imported ontologies.

As a further gimmick we display the defining ontology next to the sentence (unless it is the ontology we are currently viewing).