Wayland menus

[leolost2605]

This removes the gala-daemon autostart and instead starts it as a wayland client on wayland or as a normal subprocess on x. It therefore also removes all the session stuff (not sure whether we have to do somewhere else something else too).

It spawns a transparent window that covers the whole display and makes it responsible for positioning the menus.
This is done in preparation for the wayland transition.

This currently fully works under X but doesn't work under wayland. The reason for that is that on wayland gtk always closes menus automatically/doesn't even spawn them if they are opened without an event. However this would/will be an easy fix with popovers but for now they can't be used as context menus because in gtk3 they always draw an arrow. So I would argue this doesn't block since positioning etc. on wayland works and there is no change in x behavior

Hide whitespaces might help for reviewing since some namespaces were changed to inline
Probably fixes #1826

[leolost2605]

This currently fully works under X but doesn't work under wayland. The reason for that is that on wayland gtk always closes menus automatically/doesn't even spawn them if they are opened without an event. However this will be an easy fix with popovers but they can't be used as context menu in gtk3 because they always draw an arrow. So I would argue this doesn't block since positioning etc. on wayland works and there is no change in x behavior

[danirabbit]

Don't forget to add the new BackgroundMenu and WindowMenu files to POTFILES :)

[danirabbit]

afaict this works exactly the same on X11. My wayland session is crashing right now so couldn't test that 😅 Would love an ack from @tintou or @lenemter so we can move forward :)

[lenemter]

I haven't tested it with multiple monitors (yet) but still it looks very good. I left some code suggestions, after fixing them I'll happily approve this branch :)

[lenemter]

Code looks good.

There is one thing that bothers me, you can switch workspaces while the menu is open. We should probably close the menu or disable workspace switch while the menu is open. This should be fixed later.