Change the shadow map frustum calc.

Use a simpler shadow map center algorithm, reduce tendency for the frustum
bottom to pop out of distant terrain.  Allow terrain to self-shadow,
although the current map is not big enough to effectively allow this.
Create Xbox 360 projects.

Add the csproj files for Xbox 360, and fix the build errors caused by
.NET methods that are not supported on Xbox 360.
Fix quadtree yMask = -1 bug.

Fix quadtree search bug when yMask = -1 by using uint type.
Reduce scope of some member level variables in SceneManager.
Rename Xbox csproj files to be more git Bash friendly.
Improve terrain render performance.

Calculate exact bounding boxes for terrain sectors to improve quad tree
efficiency. Also tweak some terrain scales to reduce vertex load on GPU.
Finally, fix bugs with XZScale terrain processor property.