[Webhook] Remove from Podfile.
[Webhook] Remove webhook worker.
[Webhook] Rewrite webhooks to use a more standard parent-child-executor pattern.
[Webhook] Setup webhooks early on.
[Webhook] Trigger webhooks after commit on PodVersion.
[Webhook] Setup in init.rb.
[Webhook] When URLs are updated, stop and restart child thread.
[Webhook] Adapt spec to fit new API.