python2+3 compat
After a long last here it is - the project is python2+3. Every toggle and option in the UI has been tested ... even the tests pass.
Huge thanks for Ryan on the add-on fixes. I've squashed some of this fixes into the semi-broken commits of mine. While on others I've added a bit more to the commit message.
This replaces !6 (closed) !7 (closed) and !8 (closed)
I've been running this for about two weeks. Since Andrej is doing work on converging with upstream, I suggest merging it in a week (say 19th Mar) so that it's less hairy for him.