Added the new CategorySummary, which resembles the ExerciseRoundSummary. Added category summaries to the CourseSummary. Added categorized total points to the course instance view.

This commit is a working draft.
Merge branch 'LearningObjectCategory' into course_module_points
Merge branch 'master' into course_module_points
CAUTION: Includes a simple schemamigration.

Added points_to_pass to categories.
Added separate score boxes for each category. They also display the new category points_to_pass as a stripe if it's bigger than zero.
Improved visualisation for categories' point bars in the course instance view.
Merge pull request #66 from Rubinous/course_module_points

Points for Categories