676 translate sentences

Shall fix #676 (and #642 by extension).

Should probably also fix #664 (inclusive) **or** #655 because of 1391992cffbb2ef87301e3876ab7c24e99df039d.

This introduces sentence translations, which would allow us to translate sentences along entity/symbols mappings. It also includes support for the *logic-translation* hets hack, which would allow to translate
sentences along logic-mappings if the imported ontology is of a different logic than the base ontology.