Removes the floor node in favor of wall node

From a .tmx perspective, there is now no difference between objects on the "floor" layer as the "wall" layer
I have retained the ability to use the "floor" layer for backwards compatibility.

Maybe someday when the project is abandoned i'll go back and clean up the layers, but it should have very little effect on performance.
typo
Merge pull request #831 from jhoff/removing_floors

Removes the floor node in favor of wall node