Make an GUI to add custom themes

[codic12]

It's not hard to make a GUI to do this, if we can with plugins. Not sure why #146 was closed...
For example, I'd like to see Qogir, but I don't know how to make a plugin. The same goes with the OSX Gtk themes.
Finally, can we add an option to change the titlebar buttons in the headerbar? The close, minimize, and maximize buttons, at least in Materia, get the buttons from the icon theme... a feature to add custom SVGs would be greatly appreciated, by me at the least...

[codic12]

What's good first issue @actionless ?

[actionless]

as i'm not using any of the things you listed i don't have any interest to work on them, so it could be a good first issue for a new contributor

see also: https://help.github.com/en/github/building-a-strong-community/helping-new-contributors-find-your-project-with-labels

[actionless]

also i recommend to change the issue headline to be more descriptive

[actionless]

duplicate of #33