Make plot labels in training evaluation more general

Currently, the code assumes that we train with ttbar and Z'. Therefore, the labels in all the plotting code I've seen are hardcoded like for example here in the PlotAccuracies function.

Since I do not use Z', I'd like to be able to change that plot label (for many other plots as well).

This is related to #106 (closed) which asks for an even more general approach of having the option of >2 different validation files. Maybe we could have a structure like the following in the Training config:

We will create a new protected branch, where the changes will be merged in.

• @birk will start reworking the validation process, so that we have the following structure:
• @alfroch will implement the corresponding changes for the testing process

# Add training file
train_file: <path_palce_holder>/PFlow-hybrid-preprocessed_shuffled.h5

validation_files:
    ttbar_r21:
        path: <path_palce_holder>/MC16d_hybrid_odd_100_PFlow-no_pTcuts-file_0.h5
        label: "$t\bar{t}$ Release 21"
        data_set_name: "ttbar_r21_validation"

    zpext_r21:
        path: <path_palce_holder>/MC16d_hybrid-ext_odd_0_PFlow-no_pTcuts-file_0.h5
        label: "$Z'$ Release 21"
        data_set_name: "zpext_r21_validation"

The test block will be changed equally to a similar format:

test_files:
    ttbar_r21:
        path: <path_palce_holder>/MC16d_hybrid_odd_100_PFlow-no_pTcuts-file_1.h5
        label: "$t\bar{t}$ Release 21"
        data_set_name: "ttbar_r21"

    zpext_r21:
        path: <path_palce_holder>/MC16d_hybrid-ext_odd_0_PFlow-no_pTcuts-file_1.h5
        label: "$Z'$ Release 21"
        data_set_name: "zpext_r21"