Everyone knows about the Academy Awards. But have you heard of the "Mini-Oscars" given each year to new movies by students? The seventh annual Student Film Awards were recently bestowed, and the winners are an impressive lot, auguring well for the future of American moviemaking. The fiction prize went to Candy Store, by Claude kerven of New York University. A 30- minute melodrama about a backward boy whose brother is mixed up with the mob, it's as tight and professional as many a Hollywood offering. The winning documentary, Karl Hess: Toward Liberty, by Roland Halle and Peter Ladue of Boston University, is a fascinating glimpse of a fascinating political thinker. In addition, experimental and cartoon prizes went to young filmmakers from California. As cosponsors of the awards, the motion-picture academy and the Bell System are to be thanked for supporting the future of film in so concrete a manner and congratulated for unearthing such strong-winning films for 1980.