Camera flights

Start of #1188 that also turned into part of #1060.  More to come; no need to increase the scope of this.

* Replaced `CameraFlightPath.createAnimation` with `Camera.flyTo` and replaced `CameraFlightPath.createAnimationRectangle` with `Camera.flyToRectangle`.  Code that looked like:

            scene.animations.add(Cesium.CameraFlightPath.createAnimation(scene, {
                destination : Cesium.Cartesian3.fromDegrees(-117.16, 32.71, 15000.0)
            }));

    should now look like:

            scene.camera.flyTo({
                destination : Cesium.Cartesian3.fromDegrees(-117.16, 32.71, 15000.0)
            });

* Renamed `options.endReferenceFrame` to `options.endTransform` in `Camera.flyTo` and `Camera.flyToRectangle`.
* Updated third-party [Tween.js](https://github.com/sole/tween.js/) from r7 to r13.