testing/*: adopt abandoned packages

Take over maintainership of packages I use in Testing to ensure they don't get dropped.
I will also setup release-monitoring.org associations for them, if not already done.
As before, I do not feel comfortable in community or main yet, but I think some should go there,
so I might want better folks to grab some of these to move later.
```
ardour
freedoom
game-devices-udev
gnome-latex
mint-x-icons
mint-y-icons
onevpl-intel-gpu
thermald
wine-mono
xdg-user-dirs-gtk
xed
xfce4-mailwatch-plugin
xfce4-mixer
```