Remove SwipeableItem.js from onyx WIP since it's superceded by swipe support built into enyo.List

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@palm.com)
ENYO-1868: fix onyx.FlyweightPicker to be more careful in using null/undefined values for selected.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@palm.com)