config: Allow overriding touchpad state

[Drakulix]

Touchpad toggle functionality for #732 via cosmic-config.

@ids1024 This needs obviously a new system-action as well, but otherwise is this enough for cosmic-osd?

[ids1024]

On Gnome, the fn key seems to toggle the dconf key /org/gnome/desktop/peripherals/touchpad/send-events, which is also toggled by the Touchpad toggle at the top of touchpad settings in gnome-control-center (which makes the other controls on that page insensitive).

If we want something similar to Gnome, it would probably make sense just to use state in the input_touchpad config of cosmic-comp? cosmic-settings could also get a toggle for this on the touchpad settings (which we don't currently seem to have).

[Drakulix]

If we want something similar to Gnome, it would probably make sense just to use state in the input_touchpad config of cosmic-comp?

Then a device-specific config could override it. That is why I went with a separate config entry.

[ids1024]

Yeah, I suppose if we ultimately want to expose per-device settings in Cosmic Settings, we'd expect the touchpad toggle key to work even when the touchpad has its own configuration.