(#16, #17) add application setup form

* add user_interactions layout
* add setups resource, controller, view to let admin to configure app in browser
* add Setup class to create default company
* show company settings for admin
* move gitlab settings from ENV to DB
* move welcome/signin to sessions/new
* add rake task github_gitlab_configs:from_env_to_default_company
* fix associations
* fix migrations and fix tests
* add Capybara gem
* add first feature tests