- Migrate `.codeclimate.yml` to version 2 structure
- Disable Code Climate [maintainability checks][]

https://docs.codeclimate.com/docs/advanced-configuration

[maintainability checks]: http://blog.codeclimate.com/blog/2017/10/12/10-point-technical-debt-assessment

This commit upgrades the Code Climate configuration file and disables
the new maintainability checks.

Once this PR is merged, we can experiment with the new checks via pull
requests (the PR will report new issues) or via the [Code Climate
CLI][cli], which [now also supports the new maintainability
checks][cli-support].

[cli]: https://github.com/codeclimate/codeclimate
[cli-support]: https://codeclimate.com/changelog/5a0e488824cfa902a300091c

* add scss_lint to Gemfile

* add .scss-lint.yml

* fix warnings of scss-lint

* chmod -x styles/variables.scss

* Enable CodeClimate SCSS Lint checks

* add brakeman to Gemfile

* Enable CodeClimate brakeman checks

* add config/brakeman.ignore

* add bundler-audit to Gemfile

* Enable CodeClimate bundler-audit checks

* Exclude javascript locale files form Code Climate's duplication
  engine. It is silly to have duplication check with locale files.
  They are supposed to look similar.

* Prevent unnecessary blocking for translation updates (like #1661)

Created a .codeclimate.yml configuration file that will work with your existing configurations for ESLint and Rubocop.