Start.py: minor improvements

-Check if gngeorc and dgenrc exist. 
-Fix hotkey button.
-Change special button key binding:
select+start = exit
select+l = load state
select+r = save state
select+left = last state
select+right = next state
select+x = RGUI
select+b = reset
Start.py: use global home path variable
Merge pull request #280 from gizmo98/patch-2

Start.py: minor improvements