Dan Sidner grew up in Kearney, Neb., but gumbo runs in his veins. Buy him a plane ticket to New Orleans, put a drink in his hand when he gets there and he is one happy man. Fortunately, Sidner co-owns Maxie's Southern Comfort, the popular Milwaukee restaurant that specializes in the Cajun and Creole cooking of Louisiana as well as the food of the Carolinas "low country." Maxie's has big plans for tonight and tomorrow.