So informal were this year’s Boston Music Awards that it almost didn’t seem to matter who won. They were once a more ornate affair held at either the Orpheum or the Wang Theatre, but last night they took place for the second time at the Avalon club. The mood felt more like a backyard barbecue and a rare unity was enjoyed between the city’s many musical factions. Winners and presenters ranged from Keith Lockhart of the Boston Pops to hot local rockers Dear Leader and Lost City Angels, plus senior-citizen bluesman Weepin’ Willie, who won a lifetime achievement trophy.