Merge train executables and make the LR Reducer configurable

This MR adds the following:

• Removed the executable part of the train scripts and created train.py which is now the executable.
• Added a flag in the train_config which has the tagger name in it. With this, the scripts can work without relying on the args input which tagger was used. The args options is still there but not with --dips or --dl1. Thats now the -t or --tagger option.
• Changing the --dips etc. to --tagger dips for plotting_epoch_performance and evaluate_model.py.
• Added another flag in the train_config to make the Learning Rate Reducer configurable. You can set all the parameters in the NN_structure if you want to. Otherwise the current hard-coded values are used as default.
• Renamed and moved the old train_*.py with the models and all inside to a folder called models. There you can change everything you like (just to clean up and sort everything a bit).
• Adapted the unit/integration tests.
• Added the changes to the docs.

closes #81 (closed)