minor fixes
moss integrated
fix activity bugs
added Assignment::is_submitted_by method
fill course/admin
profile fixed
profile fixed
final: assignment manage, many bugs
another way to add MathJax.
assignment management: submission numbers
statistics; course destroy fixed
add announcement
deal with notification.
zip download bug fixes
finshed notification.
multiple bugs fixed; password change
real final: announcement
deal with message.
merged with announcement.
merged i18n.