shouldRespond handler for twitter interactions

[lalalune]

Right now twitter responds to every message in every thread, which is annoying some people and unnecessary. We should have the shouldRespond handler so Spartan and others check if they should respond before forcing a response. We do this in the other clients, so it should be easy.

[lalalune]

@dreaminglucid @alextitonis the code is right but it just kind of sucks in implementation a bit... always responds. I'd like to have it like posts instead, maybe? Or have the option of replying OR liking, and indicate in the prompt that it should reply, like or like and reply.