Added Upgradable Switches - #331

Switches can now be upgraded by inserting a CPU or Ram. These have the following effects:

Ram: Message Queue size gets increased by 5 per tier (T1 => 25, T1.5 => 30 etc) effectively allowing up to 50 messages instead of 20  
CPU: Message delay gets reduced by one tick per tier allowing to reduce from 5 to 2.

Do not close the issue please (or reopen if autoclosed) since i am still going to improve the GUI
What about the 'readable' part, though? It would make the code more easily understandable without having to know anything about how the inventory is layed-out, I think? (That was actually my main point, should have made that clearer.) Or in other words, this has a faint smell of 'magic numbers' for me ;-)