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 is an incomplete cleaned-up continuation of Lisa Neigut's push
notification bouncer work. It supports registration and
deregistration of individual push tokens with a central push
notification bouncer server.
It still is missing a few things before we can complete this effort:
* A registration form for server admins to configure their server for
this service, with tests.
* Code (and tests) for actually bouncing the notifications.