Take advantage of the docker cache for a faster docker build

Moved the install script (for both the binary download and the bundle install) to before the ADD assets/ step to take advantage of docker caching system for more detailed explanation see http://ilikestuffblog.com/2014/01/06/how-to-skip-bundle-install-when-deploying-a-rails-app-to-docker/

Also removed the copy default configuration step from the init script (again to make the docker caching system work) as this step is repeated in the init script.