Datepicker improvements

[mmouterde]

• A datepicker is about 200 bindings. On a page with many datepickers (20 in my use case) this amount of bindings has a real impact on performance.
  • I suggest to add a boolean lazyDom parameter to datepickerPopupConfig. When this parameter is true, the datepicker popup Dom and bindings are created on focus and deleted on blur.
• The datepicker popup root element (UL) has no attribute or class to allow jquery/angular.element selection
  • I suggest to add a 'datepicker-popup' class to this UL element

[ilanbiala]

This seems like a good idea, though a collab should review it to make sure that the logic works out.

[chrisirhc]

Thank you, but #1915 is a more complete version of this improvement. Please review and test the logic there instead.