Framework drag driver now sends new event type - exited window.

When drag exits Launcher window (for example, goes to Shelf) launcher doesn't get notified
and thinks the drag is still over it. For example if there is a moved shaking icon in Hotseat,
it will keep shaking.

Fixing this.

Bug: 22028725
Change-Id: Ie57572a57a324d426c9f6e57dc0bba56630e92df