Discard the time component in min/max date setting to include same-day selection

To reproduce the issue, call `setMinDate()` or `setMaxDate()` with a time component. For example, use `moment('2014-06-01 06:00")`. When you select from the calendar 2014-06-01, you'll notice that 2014-06-01 is disabled.

Fixes #409 and #337