This adds a frontend for the analytics system we've had for a few
months, showing several graphs of the data in Zulip.
There's a ton more that we can do with this tooling, but this initial
version is enough to provide users with a pretty good experience.
Fixes#2052.
This adds some configuration options to settings.py, namely
PASSWORD_MIN_LENGTH and PASSWORD_MIN_QUALITY, which control
when the frontend validator invalidates the password.
Closes#2628