Prefab replacements with no game object

[Alkanov]

Prefab Replacement setting allows you to set a Tiled Object Type name while leaving the GameObject part empty, then SuperTiled2Unity ignores it.

What I have done here allows you to set a Tiled Object Type and by not selecting a GameObject to replace it with, you can ignore the whole Tiled Object Type. This is particularly useful when you want to have 2 different behaviors on two different Unity Projects but with the same Tiled Project.

I know this could be achieved with CustomImporters but I also feel like this is the "right" behavior when you are allowed to set a Tiled Object Type and leave the GameObject section null

Related to https://github.com/Seanba/SuperTiled2Unity/issues/132