fixing an issue with drupal_add_css and the omega base theme files that can be selected in the theme settings to load.
Also fixing readme.txt files with correct path to configure sub-themes (minor)
This is mainly a port of ThemeKey 6.x-3.0 to Drupal 7 with minor improvements created at the Drupal 7 Sprint Camp in Hannover (Germany) on the 16th and the 17th of October 2010 by Carsten Müller, Christian Spitzlay and Markus Kalkbrenner. (Thanks to Eugen Mayer for the JavaScript support)
In addition ThemeKey Properties has been merged into ThemeKey.
Right now it's not heavily tested, so feedback is welcome!