- Move container opening (and gui handling) into a separate class
- Move turtle/computer placement code onto the block
- GUIs now use gui{Left,Top} instead of calculating it manually.
- IPeripheralTile is now exposed in the API.
The main aim of this is to allow for greater extensibility for other
mods. For instance, you can now prevent turtles placing dirt blocks, or
turning when on gravel.