set ontology_id of translated sentence correctly

The ontology_id of translated sentence should
equal the ontology_id of the underlying sentence
and not the origin of the mapping.

This is because there could be multiple mappings
without a sentence-definition in between.
add migration to reset translated ontology_id

For TranslatedSentences the ontology_id should refer
to the origin sentences ontology_id (it should
basically be a shortcut).

The migration will take care of that. However
there is no reversal for this particular migration
as the erroneous data is 'lost'.
Merge pull request #976 from ontohub/936-readjust_origin_of_sentences

936 readjust origin of sentences