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 adds the data model and bugdown support for the new UserGroup
mention feature.
Before it'll be fully operational, we'll still need:
* A backend API for making these.
* A UI for interacting with that API.
* Typeahead on the frontend.
* CSS to make them look pretty and see who's in them.