Add missing keybinds in Help > Keyboard (Mute and OSD)

[YarnSphere]

Adds the "O" (OSD) and "M" (Mute) keybinds to the keyboard help section.

I edited all existing language files even though I only really know english; for the other ones I used online translators so the strings may be slightly off.

Pinging some translators to confirm the strings I added (hope that's okay): @driet, @jairbubbles, @KasperZutterman, @Etharr

[YarnSphere]

Thanks! The one I'm most doubtful about is the polish "mute".

[driet]

German/de is fine. OSD is common, too though.

[enen92]

@jairbubbles translations are now handled in weblate. Please go ahead and contribute the changes: https://kodi.weblate.cloud/projects/kodi-web-interfaces/chorus2/

I'll make sure the translations are merged before bumping chorus2 for nexus final.

[jairbubbles]

Thanks @enen92 but I'm not finding any of the strings in weblate so I'm not sure how to help.

[enen92]

Nevermind @jairbubbles, my fault. This only affects the readme markdown files so they have to be contributed as a pull request. Can you do it?

[jairbubbles]

https://github.com/xbmc/chorus2/pull/528