Partial refactoring of exercise code into Backbone views.
Merge branch 'backbone' of https://github.com/rtibbles/ka-lite into backbone

Conflicts:
	kalite/distributed/static/js/distributed/exercises.js
Initial integration of exercise's Backbone models into its views.
Simplify exercise_handler to pass only needed info.
Style "Practicing" portion of title less emphatically.
Fix to student_log_api to pass *args and **kwargs to decorated view.
Fixes to user exercise data API calls/endpoints to get data loading.
Create 3 different models when instantiating an ExerciseWrapperView.
Allow JsonResponse to take a Django model as input, serializing it.
Properly handle form submission (e.g. by "enter" key) for exercises.
Fix exercise_log api call to handle GET requests properly.
Load questions by seed, and reload exercise data only as needed.
Ensure seed is initialized in khan-exercises before deciding type.
Rename "hint-remainder" to "hint-reminder".
Merge pull request #6 from jamalex/backbone

Backbone work