Problem on changing deadline time for assignment

[yangsong8]

This bug is found when we tried to input deadline manually to a new assignment.

Usually we left click on the textfield to edit a deadline and a small pop-up window will show up. And then we can press 'Esc' to get rid of this window and type the deadline manually.

But today we found we cannot change the time zone manually from '+0000' to'-0400', every time we tried to change the timezone it would flash back to '+0000' immediately. It seems the timezone '-0400' is not a valid input.

[efg]

Another problem is that only US timezones are listed (though Alaska and Hawaii are not).

Also, the date/time picker is unaware of daylight savings time. It always uses standard time (e.g., Eastern = -0500). This must be fixed. Having times be off by an hour is as bad as having them be off by 5 hours (which was the case when it always used UTC).

Furthermore, the code should use timezonepref for the current user, and default to the user's preferred timezone (I shouldn't have to scroll down to "Eastern" every time I create an assignment).