Draft: Restructuring production interfaces

Changing the way interfaces work in generation by adding new interfaces (and changing existing ones):

• A new IProdTool that deals with all the generation steps from hard process up to hadronization (except decay) by calling the following intrefaces.

• IHardProdTool that takes care only of the hard process generation step (implemented by interfaces to generators such as Madgraph).

• IShoweringTool that deals with underlying event, parton shower and hadronization steps (most likely using implementation of interface to Pythia).

• Adding new ProductionWithHardME class (not anymore as a base class like in Gauss sim10, but as a working class that implements IProdTool and calls IHardProdTool and IShoweringTool)

A more detailed explanation with diagrams, and on how to test it can be found here https://codimd.web.cern.ch/JtD7xAGqS6S9eSIyfmKqRA#.

Relates to #39