Route management in RouteLayer

[jamescalam]

We need to be able to manage routes within existing RouterLayer objects. Ideally we should be able to:

• Add new routes (already partly implemented but I know for sure it doesn’t add newly added routes to self.routes attribute)
• Edit existing routes, we need to consider impact one self.index, self.routes, etc, and add tests for this - methods should allow addition and/or deletion of route utterances
• Delete existing routes

[jamescalam]

Will be closed with #437