Appearance: use settings.create_action

[danirabbit]

Fixes #429

Rebase merge/review commits separately

• Bind color scheme radios to color scheme gsetting with create_action
• Bind dark schedule radios to dark schedule gsetting with create_action

Removes a bunch of complicated touching of accounts service and simplifies settings binding. When manually changing color scheme while schedule is enabled, schedule will be snoozed instead of changed to disabled. Settings Daemon now handles setting mutter settings, syncing accountsservice etc

[lenemter]

We need to remove the old color scheme from accounts service then and update granite and elementary/greeter#786 to use it

[lenemter]

Or we can remove this from granite entirely since granite already relies on portals

[danirabbit]

@lenemter settings daemon already handles setting accountsservice when the key is changed, so I don't think there's any more changes needed here for that. It should still work the same

[lenemter]

@danirabbit I found out about this too late lol. I've already proposed to remove color-scheme from accounts service

[lenemter]

Code looks good and works as expected