[MdDatepicker] Throw events

[Tamakiwan]

I've had some people tell me that the way the datepicker saves the date on the bound variable is not intuitive, as you have to click on the "OK" button to actually select it. People have been clicking on the desired date and closing the datepicker by clicking outside of it, which doesn't actually save the selected date. Currently, there is no way to get the selected date but for the user to close the datepicker by clicking "OK".

Throwing an event onDateSelected with the clicked value and an event onDatepickerClosed would solve this problem, as these events could be listened to in order to reproduce the desired behavior, without actually changing how the datepicker works.