Adding support for "condense single date" option

This option will make the display output just display "January 4th,
2014" for example if the start date and end date are the same (rather
than "January 4th, 2014 - January 4th, 2014").  Also setting old start
and end dates on range select so that notify() is called in all
situations (had a use case where it wasn't being called when the picker
was modified outside of the picker itself).