fix(datepicker): mark input field as invalid if the date is invalid

Closes #1845
fix(datepicker): rename `dateFormat` to `datepickerPopup` in datepickerPopupConfig

Closes #1810
fix(dropdown): unbind toggle element event on scope destroy

Also, change the way disabled dropdownToggle is read from `attrs` instead of element property.

Closes #1867
Closes #1870