Allow placing items from the unloader onto building that allow that.
Merge pull request #6 from asarium/feature/hopper

Allow placing items from the unloader onto buildings that allow that.
Added design for receiver & updated design for teleporter.
Implemented Teleporter and receiver. Added additional checks for the position/rotation of the belt element (i.e. can't connect a Belt to a Belt rotated by 90 degrees anymore). Splitter does not get stuck if one branch is full, and switches back to the other one automatically if necessary.