Menu spring animation changes for opening and closing, drawer bounce indicator

- Added `bouncePullMenuWithCompletion:` to hint to the user that the drawer is openable.
@paultiarks 

- Changed the drawer animation to be a spring based animation to make it a little more natural and hopefully give some indication the content is scrollable. (https://wmobile.atlassian.net/browse/SCIPHONE-1746?filter=-1)
- Fixed some of the dragging to not exceed natural areas where they should stop.
- Fixed the calculation of the drop areas on whether to open or close. Previously dragging the drawer open at all meant it would definitely expand. Now respects the .33/.66% drop spots depending on velocity.
The - 0.5 will look fuzzy on non-retina.