The GRACER -OMNI is a prototype based on Chevrolet's Vega hatchback.    It was designed and constructed by Herbert Gracer, architect-product designer. Being a practical man, Herb Gracer has never owned a sports car!   He wanted one that would convert to accommodate additional passengers and luggage.   Confident that roost auto buyers echoed his sentiments, he set about designing the GRACER-OMNI. In the interest…