Add tests for ok.dump_tests
Initial commit for Serializable interface
Move client/utils.py into client/utils/ for now
Add separate directory for client exceptions
Add SerializeArray and SerializeMap to client
Add utils/serialize_test.py
Move client utils_test to test/utils/
Implement core models using Serializable class
Add 'should_grade' method to GradedTestCase and fix grading_test.py
Fix tests for unlock_test
Remove TestCaseAnswer
Move serialize.py to models/
Fix failing client tests related to missing type field
Rewrite ConceptCase