Added support for unprefixed pointer events (required for IE11)

With internet explorer 11, it no longer supports the MS prefixed pointer events. Instead, it supports the unprefixed version.

This pull request adds support for the unprefixed version of the events.

I also included a commit which ignores pointerdown events if the source is mouse, and mouse is disabled.

I am in the situation where I don't want the user to scroll by dragging the mouse, and I have set the option mouseDisabled.. it however doesn't prevent the user from being able to do this though, because pointerevents are still generated by the mouse