By: Addison Wylie The music in Mavis! wins us over in a flash.  I wouldn’t be surprised if filmmaker Jessica Edwards was actually tempted early on to make a straight concert film instead of a biographical documentary.  Mavis! is much more than the gospel music that enraptured listeners; including musicians Bonnie Raitt, Chuck D, Bob Dylan, and recent collaborator Jeff Tweedy (of Wilco).  The film is about Mavis Staples, the legendary singer behind a voice that…