Activate Django sites app and create a migration which adds the
LIGO.ORG domain name of the GraceDB instance as a Site. This will
be used to build absolute URIs without needed a request object.

Instantiating a new alerts app and moving the alert functionality from
events/alert.py to alerts/old_alert.py. This commit forms a starting
point where the old alert functionality is still in place and we can
rework the alert infrastructure to be more modularized, flexible,
and adapted to superevents.

Renaming LIB -> oLIB and gstlal-spiir -> spiir, at the request of
the pipelines.

django-extensions was just in the test settings before (i.e., not
deployed on production), but it is pretty nice and useful, so we
are moving it into the base settings so that it can be used
everywhere!

Adding middleware which checks the client version (for everything
under /api*) by using the User-Agent header. Obviously requires the
client to set the header appropriately as well.  Allows access
when the header is set but 'gracedb-client' is not found in it
since browsers have to access the web browsable API.

Unsure why messaging app was not enabled; it's needed for
posting flash messages about contacts and notifications.