Add GDM and Lock screen themeing

[f1amy]

For a complete GNOME themeing beauty, we should try to theme the login screen, and the GNOME Display Manager.

GDM themeing might be not possible for just an extension, but I don't know for certain.

[Py-GNU-Unix]

since gnome 42 its possible to keep an extension working in the login screen and gdm, but for gdm the extension must be installed globally(/usr/share/gnome-shell/extensions/)

https://gjs.guide/extensions/upgrading/gnome-shell-42.html#metadata-json

[ardjuh]

Simply adding "session-modes": [ "gdm", "unlock-dialog", "user" ], and installing it globally didn't do the trick, so if anyone has an idea on how to do this, please let us know or create a pull request.

[AlexMicael]

You can theme GDM with gdm-tools. I copied the shell theme to /usr/share/themes and followed the steps here: https://www.linuxuprising.com/2021/05/how-to-change-gdm3-login-screen-greeter.html

[ardjuh]

I've updated the README so it's now explained over there.

[ardjuh]

It's not that hard to do this with code, but you firstly rely on a bit to many dependencies (npm, node, sass, gsettings, set-gdm-theme, pkexec) and secondly get an authentication popup when something changes. So I don't think it is wise to code this in