Fixes bug with add flag on a page with multiple classes.
Adds class flag creation/modification time filters.
Adds flag creation and mod time uneditably to admin panel.
Fix link in flag query results when no results are found.
Adds scheduling status to flag query builder.
Improves query performance of class flag query results.
Changes flag-extra to a class rather than an id.
Fixes some more duplicate ids.
Fix class flag numbers on dashboard.

Previously they showed flags for any program.  This was not the intended
behavior.
Refactors teacher check-in

This will make it easier to add more class info to the teacher check-in page,
and maybe improve performance.  (The performance still isn't great until we
improve resources and user profiles; so it goes.)
Adds class flags to teacher check-in

Resolves #489, resolves #499, resolves #1240.
Adds more class detail to teacher check-in.
Hides class flags stuff on teacher check-in if the module isn't enabled.
Merge branch 'main' into class-flags

Conflicts:
	esp/esp/program/admin.py
Merge branch 'class-flags' into teacher-check-in
Allow volunteer registrations to be removed.

Addresses #1230.  A hidden form field has been added to mark whether the
user has volunteer shifts.  If they do, then they will be shown a
Javascript confirmation box when they try to submit a form without any
shifts.  If they confirm that they do indeed want to remove all of their
shifts, it will now allow them to do so.

For everyone else, submitting an empty form still raises a validation
error.  (All of the fields are now non-required but there is more logic in
the clean() method to compensate.)
Add a configuration/landing page for onsite class list

A simple form is shown if you don't enter any GET variables.  It then
sends you to the class list with GET variables controlled by the form.
It's pretty rudimentary.

If you manually type GET variables into the URL, the behavior is the same
as before.

Addresses #349.
Add a refresh limit

This shouldn't be necessary as the class list should be fast enough on its
own, but it's pretty easy to limit the speed of refresh.  An integer (min.
number of seconds between reloads) can be entered into the
'onsite_classlist_min_refresh' Tag.

Addresses #351.
Makes a bunch of strings into unicode

Trying to prevent unicode decode errors.
Removes reference to lists.learningu.org

Resolves Github issue #245.