Add option to turn pages with volume/page turn buttons

[lnkd61]

I think it would be nice if there was an option to allow page turning with the volume/page turn buttons on Boox devices. Would be handy to navigate through notes effortlessly without having to swipe or bring up QuickNav.

[Ethran]

My device doesn't have volume buttons, so I won't work on that.

If someone wants to contribute this, I'm open to accepting this into codebase.