Change the Retraction field to be an int (rather than a bool)
to match other "flag-type" parameters.

Since we only have one API endpoint now, we only need one skymap
URL in a VOEvent, rather than three.

Also removes need for pylal, which is no longer available.

Fixing two migrations
  - ligoauth 0004: properly delete User instance for gstlal-spiir-gpu,
    not just LocalUser/RobotUser
  - ligoauth 0013: deleted, since gstlal-spiir-gpu has been deleted,
    we don't need to create a RobotUser instance for it

Restrict access to RSS feeds to internal users

superevent_id is now always default superevent ID (SXXXXXXa),
while a new 'gw_id' field is either None or the GW ID.
We also add the 'far' field which is just the preferred event's FAR.
Finally, we remove some fields for unauthenticated users.

No point in allowing access since unauthenticated users don't
see graceids anywhere else and they can't access the events
anyway.

Adding some information for search and latest web views, and
changing what is shown to unauthenticated users.

Some changes to how information is displayed on the superevent
detail page, including different information for unauthenticated users

far: preferred event's FAR
default_superevent_id: S-type ID
gw_id: None if not confirmed as GW, GW ID otherwise
superevent_id is still gw_id if confirmed as GW, otherwise
default_superevent_id.

We had removed the ability for GraceDbModelBackend to do
authentication, but it is relied on for basic auth by the
BasicAuthentication class in django-rest-framework.  So we undo
that change and remove the GraceDbModelBackend class altogether
in favor of its parent, ModelPermissionsForObjectBackend.

ControlRoomMiddleware is a new-style middleware, but that makes it
somewhat hard to unit test.  So we just split up the request and
response processing into separate functions which are called
within the __call__ function.

Remove several features from superevents detail pages for
unauthenticated users, since they wouldn't be able to use them
anyway: tagging/untagging log messages, adding log messages, and
adding EMObservations.