It's been a while since we've seen anything new from iBackFlip, but now the company is back with its latest -- and least expensive -- bag, the TabKeeper 360 ($55). Able to be worn as a messenger bag, sling style backpack, or briefcase, depending on how you position the detachable strap, its key feature is the same as previous carriers from the company. That is, it can fold down for hands-free access, with straps holding the tablet perpendicular to…