Add integration with the vikingo-skeleton

Added the following files:

  * public/app/assets/javascripts/application.js
  * public/app/assets/stylesheets/application.css
  * public/app/template/images.rails
  * public/app/template/stylesheets.rails

The vikingo-rails-config Thor task will perform the following modifications to
the new project, after removing the default .gitignore file:

  * Replace the app/assets/javascripts/application.js file
  * Replace the app/assets/stylesheets/application.css file
  * Clone the vikingo-skeleton repository
  * Clean up the vikingo-skeleton repository
  * Move images to its corresponding directory
  * Move javascripts to its corresponding directory
  * Move stylesheets to its corresponding directory
  * Declare images in the application layout file
  * Declare javascripts in the application layout file
  * Declare stylesheets in the application layout file
  * Replace the application layout file with the newly generated one
  * Configure the production environment to serve static assets by default