Supports locked state; tweaks to iOS 7 look

setLocked shows white locked icon in track. Still have to set switch to
on and set user interaction to disabled separately.

Shadow closer to iOS 7 beta 3 look.

Animation speeds closer to iOS 7 beta 3, though not quite exact.
Fixed getter function name
Merge pull request #6 from manishvij/master

setLocked shows white locked icon in track