It's an unprecedented dedication to their craft that sets the creators of the new comic strip "MULLETS" apart from their fellow cartoonists. Our exclusive photos show the extraordinary lengths to which Rick Stromoski and Steve McGarry have been prepared to go in their quest for authenticity.     There is an old adage in cartooning that says you should write about what you know. Perhaps it is no coincidence that Stromoski and McGarry's new cartoon strip features a pair of total idiots.