Add attempeted at field in grading summary
add a new saved_at field in submission table
Add last save field to mission grading
Merge remote-tracking branch 'upstream/development' into features/mission-date
Merge branch 'features/mission-date' of https://github.com/wangqiang1208/coursemology.org into features/mission-date

Conflicts:
	app/views/assessment/gradings/_summary.html.erb
Merge pull request #200 from wangqiang1208/features/mission-date

Add attempeted at field in grading summary
remove unused code
use after_save to replace after_update and after_create
update achievement after grade changed
change user_course to student
make sure update_achievement ran before expire_fragment
remove self statement
remove update_ach in user_course, use update_exp_level instead
[Survey] change has_section to is_contest
fix survey
Merge pull request #205 from wangqiang1208/bugfixing/achievement-updating

update achievement after grade changed
Merge branch 'development' of github.com:Coursemology/coursemology.org into development
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy
precompiled assets