Preliminary fix for the "dsp on" (Ctrl+/) keybinding.

• Make the Ctrl+/ keybinding work on German keyboards. This actually adds a binding for the 7 key which has the / symbol on it as a shifted key on German keyboards. For some reason that key isn't properly mapped by nw.js, so we do it manually. We do this unconditionally, as there doesn't seem to be a portable way to check which keyboard is actually active.

• Add a secondary, more international-keyboard-friendly, Ctrl+, keybinding for the "dsp on" function. The comma works much better for this function on some European keyboards which have the / key on the first row of the keyboard, as it is next to the period on most European keyboards (the Latin ones at least). The intention here is to make it easy on a wider range of keyboards to quickly turn off dsp and then turn it on again using keyboard commands. The Ctrl+, keybinding should work well for that purpose with almost any Latin keyboard. But note that the Ctrl+/ keybinding remains to be available as well for backward compatibility.

NOTE: Right now these only work in canvas windows, we still need to add something similar to the console windows to make it work there.