Google calendar import functionality.

* Add angular factory for google calendars.  Only query functionality
  is supported.  Filters out all-day events.

* Add logic to add a "gCalStore" instance for every calendar selected
  by the . TODO: Can't remove a google calendar store once it's added.

* The "query" method of the "$tasks" service and store services now
  take a Date object for the "day" parameter instead of a string
  representation of the date.