Visual rearrangement

Functionality exists, but notifications in the middle section don't yet show up in the proper place.
Enable use of student usernames on student admin page

This is in addition to email addresses, which also work.
Fix, and add more, tests
Enable alerts when a task succeeds.

Note: Alerts are pop-up boxes. Not sure if this is desireable, but I couldn't figure out
how to make a success message show up in the same place that error messages do.