packagekit: Workaround PkControl main context assignment
The PkControl has signals for the repository changes and update changes,
which the plugin connects to, but those are never delivered, because
the main context used for the D-Bus signal delivery is not the main
context, but one pushed as a thread default from the pk-control-sync.c.
It's even worse, because the GDBusProxy under the PkControl is created
on demand, with no way to create it.
gtk-style.css: Change margin for adaptive-symbolic icon
The margin is used to draw the icon rectangular, instead of square,
but gtk4 claims a runtime warning due to too large margin:
> Gtk GtkImage 0x889cf80 (image) reported min height -1942, but sizes must be >= 0
where the -1942 = (-999) + (-999) + 56. It's not needed to use such large
margin, especially when the code sets the image pixel size to 56, thus
split the pixel size evenly in the margin.
packagekit: Ensure update is prepared when all packages are downloaded
Having all packages for update downloaded doesn't mean the update is prepared.
As the "all downloaded" state is used to recognize that difference mark one
package for a download, thus the update created the required prepared-update
file, when it does not exist.
