The code is there and it compiles but breaks when you try to add any entity for reasons unknown.

The static addSphere, addBlock, and addRagdoll methods were changed to non-static to work with the new stack (necessitating other edits).

As a test I changed the control for addSphere to instead removeLast, as I didn't want to try to add to the UI.

The new classes as EntityStack and StackNode.  They have yet to be properly unit tested, but they are relatively simple.
IT WORKS NOW!

RemoveLast() is now keyed to the former addCube() button until the UI can be updated.
Merge pull request #24 from EricMeissner/master

Track and remove entities using a stack