Draggable toggle

[mlynch]

An implementation of a draggable toggle switch that behaves like iOS's. This means the bar doesn't move with the finger, but it does slide over when the drag hits a certain threshold.

One other interesting thing about the toggle is that it "tends toward" the initial state it was at before the drag started. So, if the switch was "on", the drag will need to go further in order to switch it "off", and vice versa. This is how the iOS 7 slider works.

A few more tasks:

• stop scroll dragging when dragging toggle
• Do we want to have a "hold" state like iOS 7?
  • I added a slight darkening to the toggle when holding. Thoughts?
  • Try graded browser styles
• Test on Android
• Check performance/DOM stuff. Check if should use requestAnimationFrame
• Extend draggable area to make it easier to hit
• Slow down the toggle animation speed
• tap inputs test
• Disable works