Preparations for terrain generation.

* Added newer version of TTD.Dependencies again, because somehow you reverted them after PR2 merge.
* Added PlayGameState, available from MainMenuState via. F1 key.
* Added TTD specific base class for GameStates.
* Added InputProvider which allows binding commands in GameStates. Currently escape key switches between states.
* Added World, WorldChunk and WorldRenderer classes which will hold world info in the future.
* Started with simple Gradient noise to give some visual output.