browserTrigger doesn't support TouchEvent.

[munet9]

browserTrigger in ngScenario is very useful to triggering UIEvent and used in many spec files.
But browserTrigger(element, 'touchstart'); is triggering MouseEvent instead of TouchEvent.

This causes ngTouch tested uncorrectly.
TouchEvents has no clientX, clientY, But MouseEvent has these. So ngClick(ngTouch) with current browserTrigger will pass successfully, but with real touch-enabled device won't work.

I know Chrome, Firefox needs special flags in desktop.
Is it difficult to support TouchEvent in current browsers?

I think this fixes some issues(#2548, #3556, #4001, #4428, #4583).