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
Implement config mapper for 4 ruby rules
Introduce Hound-style default config

* Extract RuboCop configuration logic to `RuboCopConfig`
* Merge the base config specified in the review tool syntax
  with hound-specific default config