Show counts next to each day in the "Days" filter

[JasonFreeberg]

For each day of week in the Days selector, show the number of schedules with events on that day. Example:

  [_] Monday (23) 
  [_] Tuesday (4) 
  [_] Wednesday (23) 
  [_] Thursday (6)
  [_] Friday (3)

The schedule objects have a property with a list of days, so we just need to run a mapreduce over filteredAndSortedSchedules.

Optional: Can we disable the checkbox for a given day if every schedule has an event on that day? For example, if every schedule has a lecture on Mondays, then we should prevent a user from de-selecting that day.