Read path to new likelihood file from parameter file

A new reference file for the likelihood calculation was added to the parameter repository (see commit). With these commits, the path to the likelihood file is not hard coded in the CbmTrdGas class anymore, but is read directly from the parameter file trd_vXX_XX.gas.par via the CbmTrdParSetGas and CbmTrdParModGas classes. Since the CbmTrdParModGas is also used for the creation of said paramater files, it is initialized with new default path to the reference file. When creating parameter files, this path will be written into the parameter file. In analysis this path will be overwritten by the path from the parameter file.

EDIT: Pipelines were failing on macosx 11 and macosx 1015, while passing on all other systems.

When looking into the output of the failed tests from the pipelines in cdash, it was noticed that on these systems, a whitespace was added somehow to the end of the likelihood file name when it was to be opened in the CbmTrdSetTracksPidLike.cxx. Therefore the file could not be opened resulting in a fatal error.

I do not know why this happens on certain mac versions and not on others. To circumvent this issue, any additional characters will be chopped off from the file name before it is read in the CbmTrdSetTracksPidLike.cxx as follows (see commit):

    //Whitespace added on some mac versions somehow to the filename resulting in fatal error, chop away here
    while (!fFileName.EndsWith(".root"))
      fFileName.Chop();

Since the file is only opened once at the start of the analysis, this does not impact the performance.