Webhook / Integration Event bus (#499)

* First bash at an event bus for webhooks and integrations

* Refactoring

* poc

* Revert too wide ranging changes
Move to two-queues

server/services/slack/index.js

@@ -1,7 +0,0 @@
-// @flow
-const Slack = {
-  id: 'slack',
-  name: 'Slack',
-};
-
-export default Slack;