modeled lemmatization storage on document
added preprocess lemmatization for stanford
added lemmas to the current api of models, available on rich tokens
fixed tests
added migration, also a data migration that would create empty lemmas for all documents
added tests for stanford pre process
Merge branch '411-add-lemmas' into develop
added lemma support for rules
fixed rules verifier for cases where there are no evidence candidates
Merge branch '417-lemma-support-for-rules' into develop