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.