More flexible noRetrieval options in morph

The noRetrieval option now takes a string. This string can be all "all"
to stop all retrieval (even from the state object itself) or "online"
to stop querying external services, but still retrieve morphological
forms from the state ojects, i.e. the loaded document(s).
Merge pull request #132 from latin-language-toolkit/flexible_no_retrieval_in_morph

More flexible noRetrieval options in morph