KAZOO-2560: Camp-on feature

fixed pill request's issue, rebased to master

James, we've thought about your response about sending messages through AMQP and about pivot example. We think we see more generic approach here for calling apps from callflows.
We've added wapi_cf_delegate.erl for this. It resolves dependecies problem for callflow and apps. Please check if it suites well.
Maybe just print the unhandled {Category,Name} combo instead of the full JSON object? We've been bad about this; it clutters logs up pretty fast outside of testing. We're trying to kick the habit and hope you'll join us :)