Make discussion elements change color on focus

Previously, colors changed to afford interaction only on hover; now, all
elements with a hover color change behave the same way on focus.
Visual rearrangement of new dash "Student Admin" page
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.
Add more feedback for instructors on Student Admin section of the dash.
Merge pull request #1159 from edx/gprice/forum-focus-color

Make discussion elements change color on focus
Merge pull request #1155 from edx/sarina/ins-dash-student-admin-2
Add accessible labels for forum post body inputs
Merge pull request #1161 from edx/gprice/forums-labels

Add accessible labels for forum post body inputs
Ensure nav sidebar is sized correctly on page load
Fix mako syntax in rubric template.
Merge pull request #1168 from edx/fix/vik/num-results-template
make seq tooltips appear on focus

remove focus from tab when clicked
update coffeescript to dynamically render sr spans
Merge pull request #1157 from edx/adam/a11y

make seq tooltips appear on focus
Improve focus management of forums nav sidebar

Now, when the list is reset (e.g. by sorting), the first thread is
focused. When the "Load more" link is clicked, upon loading more
threads, focus moves to the thread immediately following the thread
that was previously last in the list.
code review cleanup
Merge pull request #1169 from edx/gprice/forum-load-more-focus

Improvements in forums nav sidebar
Merge pull request #1167 from edx/fix/kevin/forums_accessibility