add extraPkgs and extraLibraries to wrapAAGL

[mechan1sm]

add the ability to add extra packages or libraries to FHSEnv made by wrapAAGL
so the following snippet will be possible:

{
  home.packages = with aagl.pkgs; [
    (honkers-railway-launcher.override (prev: prev // {
      wrapAAGL = wrapAAGL.override (a: a // {
        extraPkgs = (_p: [ pkgs-unstable.umu-launcher-unwrapped ] );
        #extraLibraries = (_p: [ ]);
      });
    }))
  ];
}