Add LICENSE file to all recipes

Problem/Motivation

Drupal's General Projects do not have automatic support for adding the LICENSE to the package. It is advised to add that file manually.

Affected recipes:
https://drupal.org/commerce_recipe_core
https://drupal.org/project/commerce_kickstart_admin_ui
https://drupal.org/project/commerce_kickstart_base
https://drupal.org/project/commerce_kickstart_demo
https://drupal.org/project/commerce_recipe_user_roles