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 is a preparatory commit for using isort for sorting all of our
imports, merging changes to files where we can easily review the
changes as something we're happy with.
These are also files with relatively little active development, which
means we don't expect much merge conflict risk from these changes.
This allows us to email sets of users on a server with a nicely
formatted email similar to our onboarding emails, built off of a
Markdown template.
The code was based on send_password_reset_email, but it doesn't
replace that use case, since one cannot include special values like
password reset tokens in these emails.
