Add initializer for Visualization and Overlay repositories
user
```ruby
# encoding: utf-8
require_relative '../../app/models/visualization/collection'
require_relative '../../app/models/overlay/collection'
require_relative '../../services/data-repository/backend/sequel'

CartoDB::Visualization.repository ||= 
  DataRepository::Backend::Sequel
    .new(Rails::Sequel.connection, :visualizations)
CartoDB::Overlay.repository ||= 
  DataRepository::Backend::Sequel
    .new(Rails::Sequel.connection, :overlays)

```
assistant