Touch support for W3C Pointer Events

IE11 has dropped the prefixes for their pointer events (http://msdn.microsoft.com/en-us/library/ie/dn304886%28v=vs.85%29.aspx)
pointerEnabled (and the prefixed msPointerEnabled are deprecated, and have been replaced (http://msdn.microsoft.com/en-us/library/windows/apps/hh972607.aspx)
It is ensured that only one of the pointer event types (prefixed or un-prefixed) are registered, to avoid double event firing in IE11.

Fixes #343