Change the default behavior of Program.getTimeSlots()

Now that we have teacher training and interviews in the mix, there are a
lot of time slot types we usually don't want.  In fact, usually we only
want the class time blocks.

This commit changes Program.getTimeSlots() so that the default behavior is
to filter only class time blocks, but you can provide a list of time slot
types to include or exclude.  The associated Program.getTimeSlotList() and
its invocations are similarly updated.
Remove extra GetNode imports
Remove GetNode references that were causing profile errors
Add missing cache dependency for JSONDataModule teachers() view
Remove DataTree usage from teacher class submission code
Fix typo in volunteer signup template
Fix ESPUser.user_can_edit_qsd() for class-specific QSD pages
Remove permissions check in qsdmedia view

We don't have permissions on static files anymore.
Update the event type used by ProgramFrameworkTest

This matters now.