Removed encode_id and decode_id methods, which were generally bad idea.
Merge pull request #97 from Rubinous/removing_encode_id_and_decode_id

Removed encode_id and decode_id methods
Merge branch 'master' into deadline_deviation_without_ui

Conflicts:
	exercise/exercise_models.py
Merge branch 'deadline_deviation_without_ui' into max_submissions_to_exercise_info