We're migrating to using the cleaner zulip.com domain, which involves
changing all of our links from ReadTheDocs and other places to point
to the cleaner URL.
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 fixes exceptions when sending PMs in development (where we were
trying to connect to the localhost push bouncer, which we weren't
authorized for, but even if we were, it wouldn't work, since there's
no APNS/GCM certs).
At the same time, we also set and order of operations that ensures one
has the opportunity to adjust the server URL before submitting
anything to us.
