add a function to get previous code
parse more info to _do_coding partial
auto restore previous code in training
fade out button after clicking run
update achievement gain date to submission date(not grading date)
refine code
split summary into 2 lines
remove unused code
use after_save to replace after_update and after_create
move js code to trainingsubmission.js
update achievement after grade changed
change user_course to student
modify code to support mutiple partials
 refine coding style
change hint text
make sure update_achievement ran before expire_fragment
remove self statement
change activerecord code to sql statement
refine code
remove update_ach in user_course, use update_exp_level instead