clean up loading

[jpata]

• generate more CMS training data, deploy datasets v.1.7.1 to EOS
• speed up CMS tfds production (slowness from np.append_fields)
• speed up inference code (slowness from awkward.from_iter)
• improve plotting style
• fix start epoch overlapping with the previous epoch when loading a model and continuing training
• fix model loading, do not create empty experiment dirs when not needed (e.g. evaluation)