Bug fix and css compression improvement

We have noticed an issue where the environment is added as a variable but the default configuration never makes use of that variable and always sets to :development, therefore when we access the environment in our external config.rb it is always development.

Also as we set grails.assets.minifyCss in our Config.groovy it is not used by the sass compiler, so we added this functionality.

Added an example of how to access the environment variable in a config.rb file