padOsd: Add support for setting modes for tablet buttons.
I want to be able to use standard tablet buttons with mode modifier. In gsettings it will look like: /org/gnome/desktop/peripherals/tablets/xxxx:xxxx/buttonA-mode-0/
I want to be able to use standard tablet buttons with mode modifier. In gsettings it will look like: /org/gnome/desktop/peripherals/tablets/xxxx:xxxx/buttonA-mode-0/