feat: support mouse forward/backward buttons

[jsphj]

A small addition to support navigation with the forward and backward buttons on mice and other hardware using the Electron 'app-command' event.

[sentialx]

Did you test that it works? Because last time I checked the app-command event didn't work, instead I did a workaround using event listener in the preload script.

[jsphj]

You're right, it seems to not work correctly. The preload script implementation wasn't working in the release I downloaded. When I tried adding the app-command to the code I mistakenly thought my code was working when it was actually yours 🙃 Sorry about that.