Securesync refactor

Remove all dependencies but `annoying` and `fle_utils`.

Some challenges:
* `VERSION` is now attempted to be imported in one place, and referenced from there only.  If `version.VERSION` is not found, then a dummy version (`"1.0"`) is used.
* securesync authentication should not reference the `facility`; currently I made it reference `login_required` (Django users only).  This needs to be fixed in the near future, I will open an issue for it.  But some authorization method must be implemented without specific reference to the `facility` app.
* the `crypto_login` method doesn't belong here, and was moved to the `distributed` app.