Fix databag item update for recent versions of chef (>10) and add commis/wsgi.py

Here's a fix for the databag item update bug discussed in Issue #13 (https://github.com/coderanger/commis/issues/13).

I also added wsgi.py... it can't hurt !  ;-)

ps: I pushed 2 untested and buggy commits before getting the thing to work in the 3rd commit.  I know I could hack around the git history to remove these, but I don't have much time, so I hope you won't mind.