Get emulation of LEDs & Switches working

[mithro]

They are just memory mapped io, but need to figure out how to actually display the output somewhere.

[mithro]

@shenki - Any thoughts about how this should work? You mentioned that this was also needed for https://github.com/im-tomu emulation too.

I assume we want to eventually pop up a graphical representation of the FPGA board and let a user click on the buttons / switches (plus see the led outputs).

Do you know of any existing targets which do things like this that we could copy?