#18 Add savestate capability to gamepads

[jlocke]

Much in the way gfuel allows quitting an emulator using the gamepad, we should allow users with overly advanced gamepads to save and load state within games. For example, when playing NES with a Playstation controller, perhaps one shoulder button could be used for savestate, and the other for loadstate.

Obviously this is done on a per-emulator basis, so we will likely require a means to translate a gamepad press into a keyboard stroke, corresponding to a specific key configured in GFuel. Integrating QJoypad might be a good starting point for this.