Need Improvement on Conversation.py

Need an option to enrich the Statement class. I.e. option to add additional fields.

https://github.com/gunthercox/ChatterBot/blob/3eccceddd2a14eccaaeff12df7fa68513a464a00/chatterbot/conversation.py#L24

https://github.com/gunthercox/ChatterBot/blob/3eccceddd2a14eccaaeff12df7fa68513a464a00/chatterbot/conversation.py#L48

I think slot need to be removed and serialize need to be as_dict (rather than hardcoding) or something. This allows us to inherit and enrich the existing Statement Class. Very useful if we develop any custom Adapters.

Thanks