New config syntax

Remove older configuration that using a module syntax. 
Instead, we use of the built in config settings in Rails.application.

Extensions can also easily extend the configuration by using the add_class syntax in `engine.rb` like so
```ruby
initializer "monologue.image_upload.preferences", :after => "monologue.configuration",:before => :load_config_initializers  do |app|
   app.config.monologue.add_class('image_upload')
   app.config.monologue.image_upload = Monologue::ImageUploadConfiguration.new
end
```