Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
This option provides a more convenient way to overlay dummy packages.
It also adds a function `config.lib.test.mkStubPackage` that can,
e.g., be used for `package` options.
If this commit now it is possible to define a custom theme directly
using Nix, like this:
```nix
{
programs.rofi.theme = {
"*" = {
background-color = "#000000";
border-color = "FFFFFF";
width = 512;
};
listview = {
cycle = true;
};
};
}
```
And this will be converted to the proper rasi format to be used in
rofi.
