Onsite class list tweaks

This should take care of two older issues #349 and #351:
- Shows a landing page if the onsite class list is loaded with no GET variables.  This asks the basic questions including start/end timeslot and refresh/scroll speed.
- Enforce a maximum refresh rate (default: every 10 seconds) on the server side.

The changes are quick and dirty, but I can make improvements if anyone thinks it's worth the time.