Added the construction menu and fixed some inventory issues

Hey guys,

I just added the interface for the construction menu. It was implemented, but hidden until now, because I wasn´t sure how to trigger it. So now you can change the rotation, size and place of a changed object after placing it. This makes it much easier to build your chain reaction machines.
Furthermore I fixed some issues with the inventory.

Maybe the next will be the Multiplayer feature, so tell your friends about the game ;)