Revertede students.models and courses.models.
Also deleted last migrations for both apps to avoid problems with future migrations.
Fixed faulty filtering in courses.views.
Apparently you can't filter by three custom Qs.
Fixed deadly slow show_all_course_students.
Before - 47 queries in 25.14ms.
Now - 3 queries in 2.95ms.
Improved forum_show_topic.
For FK and One-on-One we should use select_related.
prefetch_related is for Many-to-X, GenericRelation or GenericFK.
Performance improvements in students.views.assignment.
Also removed unneeded .all() in comments query.
Performance improvements in students.views.solutions.
Also removed unneeded .all() in api_students.
Fixed WET urls in forum/urls.py.
Now it follows Django conventions.
Merge pull request #21 from HackBulgaria/performance_improvements

Performance improvements