Added support to destroy daterangepicker.

In single page application where view are created and destroyed
regularly, it is important to destroy daterangepicker. Otherwise dom is
poluted with non usable daterangepicker 'container'.

This change add 'destroy' method such that it call be called anytime in
page/view life cycle to completely remove daterangepicker from dom. Note
that, it also exposes all other methods of daterangepicker.