Taking over maintainership of Breeze GTK

Ello y'all. Considering that Breeze GTK's maintainer stepped down and I've
been doing a fair amount of work related to it (yay colorschemes for GTK3),
ngraham suggested that I should take over maintainership, and that's a pretty
good idea.

So I'll be doing that idea (taking over maintainership).

I'll probably be seeing it get a GTK4 port, as well as some other things.