Minor restructuring for response creation

[domanchi]

Background Context

In my own use of this library, I structured it such that individual LogicAdapters are able to specify certain response styles, based on certain criteria. I do this by attaching additional information through the Statement object, which is passed around in a variety of functions.

Issue

generate_response in the ChatBot class overrides the resulting Statement object.

Proposed Fix

By breaking it up into a separate function, we keep the original function cleaner, as well as allows customization of the flow through polymorphism. Otherwise, we would need to duplicate a large chunk of code (the original generate_response), and this would lead to future maintenance problems down the road.