Encapsulate message posting in a queue, throttle them etc.

[Jerboa-app]

• posts should add a message to a queue for the webhook
• queue should be configurable to throttle posts (in time)
• detect dupes in some time window and discard (hashes)

IP's are throttled at root, but it's possible a spammer could repeatedly star and unstar messages and we should not assume a github webhook uses the same ip each time even if github says they do somewhere