Created by: NicolasSchnitzler
Change the way widget factory is handled:
the factory is now templated on the process type, and contains a widget for each process (identified by its address).
To reflect this change, the macro name was changed from DTK_DECLARE_WIDGET_FACTORY to DTK_ASSOCIATE_WIDGET. This macro generates automatically the abstract widget interface corresponding to the abstraction (and the trait required to use it, which the user shouldn't ever to be aware of though)
Additionally, the node now reuse the processes it has already instantiated.