Now using JodaTime for CalendarDataStore month retrieval

Also removed the isLeapYear method, which is no longer referenced.
There is a copy of this method in PhotoStore, but after this method's
removal I believe that copy to be the only version of the method.
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'