Clan-specific Integrations configuration

* Allows configuration of integration points (Twitter, CodeClimate, PagerDuty) from the clans UI.
* Stores into a serialized blob on the Clans table. Good enough for now :)
* No validation is done to ensure the provided parameters are correct.
* Everything is run from a single thor task: `thor run_integrations:run`
* By the looks of it, either the Integration classes, or the API endpoints will need to handle things already captured for Twitter mentions, Code Climate and PagerDuty Acks.