General cleanup around gestures and items

[mvanderkamp]

• Remove unused transform()
• Forward as much of the original event as possible
• Rename processSwivel -> handleSwivel
• Use type='item' since that's what the switch statement looks for
• An item is considered lockable if it has any event listeners attached
• Shorten timeout before removing swipe tail
• Optimize adding items: don't require a second packet to set sequence etc
• Send a minimal packet when asking to remove an item
• Make more use of the shared bases