Attempt to handle IE >= 10 pointer events

Using the same technique as Leaflet, this relays MSPointer events to touch
events. Using the simulator, I can verify that even pinch-zoom works with
this change, but the visual experience is a bit jumpy. Would be great if
people could test this on physical touch devices and see how it looks/feels
there.
Making buttons work

Thanks @gregersrygg for testing. With this change, zoom and other buttons
(e.g. editing toolbar) work in touch mode.
Addressing @bartvde's review comments
Merge pull request #780 from ahocevar/ms-pointer-events

Touch Navigation doesn't work in Internet Explorer 10. r=@bartvde,@gregersrygg,@mpriour