Generated by `pyupgrade --py3-plus --keep-percent-format` on all our
Python code except `zthumbor` and `zulip-ec2-configure-interfaces`,
followed by manual indentation fixes.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
This adds to Zulip support for a user changing their own email
address.
It's backed by a huge amount of work by Steve Howell on making email
changes actually work from a UI perspective.
Fixes#734.