[event-tap] Add W3C pointer event support. Fixes #1377

IE11 changed the `type` of pointer event objects from 'MSPointerDown' to
'pointerdown' to comply with their proposed W3C standard. Firefox
Nightly also supports W3C Pointer events with a
dom.w3c_pointer_events.enabled flag
[event-tap] Use window.PointerEvent for feature testing

As recommended by Microsoft in
http://msdn.microsoft.com/en-us/library/ie/dn304886(v=vs.85).aspx
Merge remote-tracking branch 'origin/tap-ie11' into dev-master
Build Event modules