Store the current language also in a class method on `Language` model.

This enables us to get the current language from any where in the app and removes the need to load the language more then once.
Adds a `ControllerActions` module, with that the `ApplicationController` will be extended.

In order to have the `Alchemy::PagesHelper`, the current `CanCan` `Ability`, the current site, language, etc, that Alchemy needs to be able to render elements and pages globally, we have to ensure that these methods and helpers are available.