MindMeld responder object should be a request object

[vijay120]

Currently, DialogueResponder has a request object as an attribute, but contains other attributes as well, like directives. However, the responder and request serve very similar functions to encode information needed by the dialogue manager to respond to an input.

Instead of the current approach, we could build an encoder method that builds a serializable responder from the same request object type with the necessary fields directives.