[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

Conflicts:
	src/event-simulate/js/event-simulate.js
	src/event/tests/unit/assets/event-tap-unit-tests.js