update view for mssion/training list.
better reg exp to filter error message when run python in path
add filter by tags for mission and training list.
Merge branch 'hung-dev'

* hung-dev:
  add filter by tags for mission and training list.
  update view for mssion/training list.

Conflicts:
	app/views/missions/index.html.erb
provide std_course id for std_answer when create submission
Merge branch 'master' of github.com:Coursemology/coursemology.org into development
fixed incomplete merge in mission/index