feat($swipe) Add config param to allow choosing X/Y thresholds.

Closes #4550
Closes #5812

- Create config parameter to pass in swipe/scroll (X/Y) thresholds.
- Allow the new thresholds to be applied to how the function determines when
to scroll and when to swipe.
- Fix bug where swiping back and forth within the thresholds would cause a bad
cancel event.
- Fix bug where if you went back inside the thresholds, you could potentially
cancel a swipe in progress.
- Add tests for all these changes.
- Clean up the docs and add definition for the parameters used in
`$swipe.bind`.
I don't really understand why we're saying "swipeThreshold only applies to movements on the X axis and scrollThreshold only applies to movements on the Y axis" --- that makes no sense to me.