Have animation frames not be trigged when not receiving device frames

Note that prior to this, every animation f
Fixes #159 unable to background after disconnect and reconnect.

Note that this simply adds a cleanup line to connection/base.js.  An
alternative and perhaps more proper way of fixing this would be to
destroy the entire connection object on disconnect, and create on
connect.
Fixes #158 setBackground unavailable; add an option controller.loopWhileDisconnected
Merge pull request #157 from leapmotion/requestAnimationFrame

[wip] Have animation frames not be trigged when not receiving device frames