Integrate Drush into UIkit

As we're nearing the first feature release of UIkit 8.x-2.0 and less focus is required on theme development, let's begin integrating Drush into UIkit for developers and themers to help in rapid development of sub-themes.

One thing I have noticed contrib modules and themes using Drush for is to create projects from the command line. I'd like to provide this type of functionality for generating UIkit sub-themes using Drush. With minimal input from the user we can then create all the necessary files needed for a sub-theme to be recognized by Drupal.

We'll start on the 8.x-2.x branch and backport to 7.x-2.x and 7.x-3.x. This means we'll eventually remove the uikit_subtheme directory and move all files in the uikit_core directory to the root directory in the repository for the 7.x branches. This will require a change record once this is committed so users are aware of these changes. Theoretically this shouldn't cause any issues, unless someone has explicitly called drupal_get_path() or manually defined the path to the UIkit base theme in their sub-theme.

I'll attempt to get this into the 8.x-2.0 feature release, which is less than a week away. If not it will be introduced in the 8.x-2.1 feature release. The 7.x branches may not see this introduced until a later date. This all depends on the time it takes to get the code committed.