Add owners

* Create owners table
* Introduce `Owner` model
* Update `Buildable#perform` to update or create repository owner
Make the buildable spec fast again
Create StyleGuideConfig model and table

* Use hstore for `rules` column to hold the hash of rules
Define default Ruby style guide config
Support fetching owner style guide

* Add route for fetching owner style guide
* Introduce `StyleGuidesController`
* Make `GithubApi#orgs` public
Support updating owner style guide config

* Add route and controller action for updating owner style guide config
* Change rules column type to json
Add style guides config ui