"Show me more results"-style templates

[gcampax]

Currently the agent will pick one, two or three results from the top of the list (depending on the parameter priority and some randomness in pruning). It would be nice for the user to be able to say, "what else you got?". This is very useful for long lists such as news or tweets.

This will need an appropriate state representation, either as a slice operator in ThingTalk, some magic dialogue act, or some other new syntax. It will also need the right runtime implementation so we push the right results to the top of the list to feed to the neural network (this is where using the slice operator is probably useful), and appropriate client-side caching so traversing a list of rapidly changing results doesn't behave inconsistenly.