fixing vmouse start/stop events to use clientX/clientY rather than pageX/pageY

swipeleft and swiperight events were being triggered when scrolling up and down large documents.

the vmouse start and stop events were using pageX and pageY, causing the delta Y to only register a few pixels. This causes the swipeleft/swiperight vertical threshold to never be met, and these events would be triggered even on swipes that were mostly in the up or down direction.

As an extra precaution, a ratio of horizontal to vertical distance could be added in the handleSwipe function, so that threshold values don't have to be hardcoded.