Splitting up much of the alerts functionality and
improving/generalizing it.

Some imports in superevents/serializers.py were moved to
function-level.  This is because several functions from
superevents/utils.py are used in the serializers for
deserialization (object creation), but the serializers are also
used in the alerts app to serialize objects to dicts.  This created
a circular import issue.

We also fix some of the reverses so that they work without a
request object being present.

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.

Now using get_superevent_by_date_id_or_404 to retrieve the superevent
for log creation via the web interface.

Created a web form and API resource for confirming a superevent as
a GW.  Also added and utilized permissions for allowing this action.

Remove commented out code blocks for file handling in
superevents/forms.py.

return 10 superevents by default for superevents list resource, instead of 3.  Matches behavior of events list resource.

fixing issue with writing event logs when a preferred event is added to a superevent which previously didn't have a preferred event