Made epic games api call response handling more flexible:
problem: product_slug location differs from product to product. Previously response parser tried to find it from single predefined path that failed for some products
resolution: using new dict_search added all known paths that could contain product slug. If no product slug is found, link to the free games offer page is added to that games heading link instead
Added 'dict_search' function for easy traversal through dictionary tree. Either returns node in given path or None
Added 'get_caller_from_stack' function to get information on where current function was called. Used for adding all relevant information to debug-log if 'dict_search' fails