Suggestion: Alter BaseSynthesizer training and generate interface to use callbacks

[mapa17]

Context

Synthesizers derived from BaseSynthesizers have the responsibility to call training and generate of the base class, which makes sure the data has specific properties.

Improvement

Instead of requiring this from the user, one could make the derived classes implement callbacks of the kind on_training_begin, on training_end, and on_generate_begin, on_generate_end, which would be called by the BaseSynthesizer.

Impact

Doing so requires the definition of 4 interfaces, that are either used to pass training and synthetic data, or class properties that hold the information.

Benefits

• A cleaner separation of responsibilities
• Provide VDL as a framework to better track Synthesizer progress (i.e. monitor and benchmark runtime)