fix code mirror rendering problem in hidden tab
remove duplicated code for activate tab
fix created qn position ( at last)
two commenting mode: per question or per submission
fix nav tab disabled bug
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy
assets precompile
clean up assignment description  html tag before saving
private files not show in work bin
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy
not remove but fade out comment box when scroll
fix mission auto grading test case result rendering js
new python sandbox

- disallowed import of potentially dangerous library
- override open so no one can modify file
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy
precompiled assets
table td vertical align middle
minor refactoring
Merge branch 'benmq/comics' of github.com:BenMQ/coursemology.org into dev/raymoond_dev

Conflicts:
	app/models/course.rb
	app/models/course_ability.rb
	db/schema.rb
	db/seeds.rb
fix comic creating new when no comics for current course
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy