Fix GaussinoExtLibs gitlab group and clean up
The custom mapping from project name to gitlab group was implemented in a number of places. Some where adapted when Gaussino was introduced, except for one place. None of the implementations was fixed when GaussinoExtLibs was added.
This MR refactors the code to have the special mapping in only one place and adds the special case of GaussinoExtLibs.
Closes #122 (closed)