Initial interaction for two state swipe to overview

> Currently swipe only works from NORMAL and ALL_APPS state
> All interpolation is spread linearly

On pausing the drag for some time, the workspace moves to overview state,
and all other transitions interpolate linearly from there over the
remaining swipe range

Change-Id: Ic79f9d0f446c9bfff11e4af4d31ddc1c86c45ab2