Add Universal Tween Engine and Camera tween

[Universal Tween Engine](https://code.google.com/p/java-universal-tween-engine/) is a library that allows values on any object to be interpolated. That is to say, values on an object can be set over a period of time, optionally following an easing equation, according to a Tween.

This PR adds the Universal Tween Engine library to the project, as well as implementing a subtle camera tween effect. The parameters of the tween can be tweaked in `ScrollingLevelScreen` to test different types of tweens and different lengths, etc.