feat(datepicker): add 'dateSelect' output for date selection listening

[maxokorokov]

Forwards date selection from datepicker to input-datepicker.
Allows to distinguish between user date selection and form control changes.

<!-- when form control value changes, ex. input changes -->
<input ngbDatepicker (ngModelChange)="..." />

<!-- emit on datepicker clicks, keyboard date selection, same date selection twice -->
<input ngbDatepicker (dateSelect)="..." />

Fixes #2181

[pkozlowski-opensource]

LGTM

[strizzwald]

Any idea when this feature will be merged in? I've ran in to a scenario where I need this functionality.

[arulananth]

Forwards date selection from datepicker to input-datepicker. Allows to distinguish between user date selection and form control changes.

<!-- when form control value changes, ex. input changes -->
<input ngbDatepicker (ngModelChange)="..." />

<!-- emit on datepicker clicks, keyboard date selection, same date selection twice -->
<input ngbDatepicker (dateSelect)="..." />

Fixes #2181

Mobile browser not getting past date.