Configure staging environment

For Heroku deployment:
```
heroku create --remote staging
heroku apps:rename ohana-api-admin-staging --app oldname
heroku config:add RACK_ENV=staging --app ohana-api-admin-staging
heroku config:add RAILS_ENV=staging --app ohana-api-admin-staging
heroku config:set STAGING_USER=username --app ohana-api-admin-staging
heroku config:set STAGING_PASSWORD=pwd --app ohana-api-admin-staging
```
create config/environments/staging.rb, copy and paste everything from production.rb, and add this:
```
config.middleware.use '::Rack::Auth::Basic' do |u, p|
  [u, p] == [ENV["STAGING_USER"], ENV["STAGING_PASSWORD"]]
end
```