added the basic functionality for showing completion status of an exercise in the TMC course page
exercise completion status calculation to moved to own class
exercise completion status calculation moved to lib
specs comleted for the exercise status generator
minor refactorings of ExerciseStatusGenerator
more refactorings to ExerciseStatusGenerator
refactoring exercise status generation: completion status passed to views as parameter and green/red bar implemented with divs
added a courses_controller spec that checks if the exercise completion status is assigned to instance variable
Merge remote-tracking branch 'mluukkai/master'
Somewhat nicer presentation of exercise completion status.
Refactored and optimized exercise completion status.

- Moved all querying from the controller into the helper.
- Got rid of N exercise object queries.
- Converted ExerciseCompletionStatusGenerator's test from
  stubs to factories.