Issue #518 with some default values
Merge branch 'database_migrations' into dev_database

Conflicts:
	tutor/db/migrate/20140323111235_create_students.rb
	tutor/db/migrate/20140323111711_create_replies.rb
	tutor/db/migrate/20140323112245_create_problems.rb
	tutor/db/migrate/20140323112347_create_solutions.rb
	tutor/db/migrate/20140323112502_create_tracks.rb