Allow dispatcher overrides in controller

@srbiv to be merged after https://github.com/bignerdranch/bnr-webhooks/pull/12

Here's a more useful diff (until rebase): https://github.com/bignerdranch/bnr-webhooks/compare/nybblr/add-inline-and-sidekiq-workers...nybblr/dispatch-overrides-from-controller