* Typed `master` to each `__init__()`.
* Having to `# type: ignore` the base class for the classes which are
"tk on darwin, else ttk" as this 'dynamic' type confuses mypy.
See the comment on `class Frame` for a suggested proper fix, which will
be more work.
First pass utilising 'futurize' to do most of the work.
There's an issue with ur'\"' in l10n.py which I'm not sure how to
properly fix.
This now has errors when hitting the 'Update' button.