Remove unused columns from sentences.
Add first draft of Theorem and ProofStatus models.
Exclude Theorem from Sentence scope.
Add Theorem route, controller and view.
Add ProofStatus model, remove STATUSES Constant.

The ProofAttempt and Theorem models now rely on this new model.
Add colored label to ProofStatus.
Add Popover for ProofStatus.
Parse Theorems.
Add specs on associations.
Add theorem parsing spec.
Use SZS ontology to create ProofStatus.
Fix seeds bug that deleted the proof_status.owl.
Create basic proof statuses for the tests.
Obey hound

In order to make the style consistent throughout each touched code file,
I also changed some lines that hound would complain about that were not
changed in this feature-branch.
Use save!
Rename module: Make it a noun instead of a verb.
Use method passing instead of block syntax.
Add comments on description and name.
Cache entities_by_name.
Rename `m` to `match`.