Fling navigation

[pdavidc]

Navigation response to user fling gestures; rotate in the fling direction with gradually decreasing velocity. From the COE requirements document:

Map engine shall support “fling” so that depending on the velocity of the users movement the globe will continue to spin for a period of time and ease to a stop.

Once the globe has stopped moving a view change end event shall be emitted

[mrdjohnson]

This is related to #15