Encapsulate Dialog Code and Decouple Core Dialog Code from Plugin

[BHSDuncan]

Is your feature request related to a problem? Please describe.
Dialog code is currently fairly tightly-coupled between the core and the chosen dialog plugin. Although this is only when it comes to "saying" something, it still needs to be addressed.

Describe the solution you'd like
Delegate/defer the handling of the "say" state of dialogs in the core code to the plugin via a created interface/contract. This interface will need to be documented as well for future implementers of dialog plugins.