Correct Facing Direction for chests & stairs & slabs

The getOppositeDirection function could probably be put elsewhere to be
reused. This one is only for 4 faces.

Partially fixes #119
I mean the message is inconsistent with the rest of the project.

Looks like it should be something like
` GlowServer.logger.warning("Interacting " + getMaterial().name() + ": MaterialData was of wrong type (" + data.getClass().getName() + ")");`