AUI-1205 - datePicker fires selectionChange event when trigger is clicked

Hi Jon,

Attached is an update for https://issues.liferay.com/browse/AUI-1205.

I made the change that Maira recommended in https://github.com/mairatma/alloy-ui/pull/84.  I also had to make a change to fix a bug I discovered when I wrote the test case.  When parsing dates from an input field, the selectionChange event was firing twice.  So I added a method that selects dates and ensures that the event will only be fired once.

Please let me know if there are any issues.

Thanks!