Add support for CMD/Meta key in place of CTRL

[bencoder]

I really struggle to get used to using control key on Mac when almost everything else uses the command key in its place.

It makes it more comfortable for me to use, but there might be something I've missed that makes this not a good idea. Happy for feedback!

[ojack]

Hi! I don't have a mac to try it on right now, but I remember there being a reason that I did it this way when I started developing hydra on a mac. (Can't remember now though!) Does the alt key still work fine with this pull request? I want to make sure we try on major operating systems and browsers before merging this.

[bencoder]

Hi! Yes the alt key still works for me. On Chrome and Firefox.

Understand completely, I don't have a windows/linux machine right now so I can't test what effect it has there.

Potential issues that I see

• Meta is the windows key on windows keyboards. Although Firefox at least doesn't treat it as meta: https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/metaKey. I'm not sure what chrome does. It seems unusual for a non-system app to respond to the windows key
• Limits potential key combo (no meta+ctrl at the same time)
• 2 key combos to do the same thing feels a little wrong :)