Changed how the PrefabReference works

I haven't touched any scenes or fixed any errors with others code so be
warned.
Merge pull request #23 from drobbs/master

Changed how the PrefabReference works
PrefabReference cleanup

I cleaned up the errors in the test class and the object holder in the
character test scene.
Proposed the solution to the error in Brent's map event class
Merge pull request #24 from drobbs/master

PrefabReference cleanup
Merging the master branch (PR#24) into the TiledTesting branch for the changes.