Makes a them inherit from another.
If an object is not found in one them look it up from the parent theme.
Makes a master them with no colors only basic layout logic
css: simply load all css in right order from parent to child. Latest change wins.
1 - refactor to make use of Theme::get_impage_PATH() that is a function that returns the image path direclty and stop using of get_image_root() . '/'
2 - makes use of virtual path and/or php script like get_impage.php?path=... That would improve performances because we can have the browser caching the image and the we can compute the exact path only when the browser tries to load it