Integration of Trd pid

[SusanneGlaessel]

The TRD pid is integrated in the following way:

The Pid framework contains two steps for the Tof pid:

1. Calculating MC-probabilities / fitting
2. Filling

The integrated Trd pid consists of three steps:
Preparation: Creating MC histograms

1. Calculating MC-probabilities
2. Filling

The preparation and step 1) are performed independently of each other for both detector pids.

Step 2) is now combined - the filling of both pids can be done simultaneously. It is still possible to run only one of the detector pids by using the same executable. The selection of what pid to run, is handled by the first argument of the executable (see README.md for more details.).

[lubynets]

Dear @SusanneGlaessel, thanks for the extensive development!

1. Please consider my comments which I left in the code.
2. Remove the files .DS_Store from the PR and add them to .gitignore so git will not include them any more (those which are already included you need to remove from git index manually).
3. Adapt the clang-format workflow to the changed naming of directories (link), and apply clang-format locally before updating the PR.

[lubynets]

@SusanneGlaessel thanks for addressing my comments!
I still have minor comments/suggestions which I left in the code.

[SusanneGlaessel]

Dear @lubynets,
thank you very much for checking the code and for your comments.
I have incorporated now everything, just that one line pid = TMath::Sign(1, charge); I left like it is (see comment). Is it ok for you?
Thank you and kind regards,
Susanne

[lubynets]

@SusanneGlaessel thanks again for the development, and for processing my comments and suggestions!