Exponentcms Exponent CMS → 2.0.1

By having the different theme styles (variations) in a folder named css_xxx, it implies that only the css files would be there. Recommend it be renamed to style_xxx and the 3 lines in the manage_themes method of the administration controller be changed from 'css_' to 'style_' this would also be in line with the convention that the 'backup' folder is names 'styles_backup'.

Furthermore, (in the switch_themes method) we should probably check for the existence of, then create the 'styles_backup' folder and 'css' & 'images' folder if they don't exist instead of asking the user to do it.