Rename AnalysableMock -> Analysable.

Mock is implied, not really a mock anyway.
Guardfile fails fast.
When model is saved creates keywords, minus stop words and downcased.

Large commit.

* Adds a wordcounts table
* Uses Concerns to associate the model with the RailsNlp classes
* Basic stop word removal
* No more duplicate keyword names.
Validate uniqueness, presence of Keyword#name