Add support for CMD / CTRL swapping on MacOS

[soywiz]

In macOS usually ctrl+c, ctrl+v, ctrl+f and the like are mapped to cmd+c, cmd+v, cmd+f, etc. some apps like Parallels Desktop do this swap too.

This adds an option to allow swapping cmd and ctrl keys.

Right now the option is not translated, and it appears in all the platforms;
we could add this option only on mac but I don't have experience with Qt, so I will need help with that.

[athei]

I think this is a great addition. The control (strg on windows) is usually harder to reach on macOS keyboards and is not used much. It would also be very helpful for games where you could then bind the cmd key which is not possible right now as it is never sent as its considered a system key. This is also why I see no harm here because without the switching the key is simply never send.

I also don't think it doesn't have to be OS specific here. The cmd key is just the windows key. Just adjusting the lable is probably fine (as suggested by me).

We could also change the option to just be: "Sent the left windows/cmd button as strg'. This would already probably be what most people want. You still keep your right windows button.

[athei]

BTW there is already a similar PR that was never merged: #1078

But I think swaping with strg is more idiomatic.