Add Exercise model.
Add route for Exercises.
Merge branch 'develop' into add_exercise_model
Add index route for exercises.
Add feature for adding exercises.
Add functionality to add exercise.

Adding corresponding controller action, view, routes.
Reduce create operation for exercise.
Add show view for exercises.
Change routing after creating exercise.
Add edit action and view for exercise.
Add destroy action for exercise.
Add form to upload Latex files.
Add function to cut Latex document into header and body part.
Switch to patched rails version.
Merge branch 'add_exercise_model' into develop