Add basic LevelDirector to create levels of varying difficulty

[piguy79]

Now that the terrain can be modified in many different ways, we need a programmatic level director to combine these modifiers in interesting ways. The level director should accept an argument to indicate level of difficulty; easier levels should use fewer modifiers with less drastic changes and more advanced levels should combine many modifiers with drastic shifts

[piguy79]

We decided to create levels by hand, but via a level editor. Do not need this.