Added basic teleporters

This might contain poorly written code, although most of it is copied from other blocks and the priority gui. Also, I originally implemented this for myself.
Basically I don't have any expectations about this being accepted. There could be much cooler teleporters, but I'm new to programming and modding, so I couldn't do something like that. 
I'd appreciate if you take a look at it so I can learn something. :)