Instead of looping over EmailMessage.send() calls, we now get the
email backend and send a list of messages. Note that the backend
sends the messages individually still but this cuts out some of the
overhead.

Some of the search utilities were still in the separate
events and superevents apps, so we moved them to the search app
and tried to clean things up a bit.  It's still kind of a mess
and probably not worth doing a full cleanup until we rework
the search.

All calls to event.graceid() -> event.graceid.

Reorganized some utility methods in the alerts app, necessitating
some changes to imports in various places.

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

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.

Updated from Django 1.11.5 to Django 1.11.14. Updated 3rd party
packages so that all of them have version requirements in
requirements.txt.  Also updated most of these packages to use the
newest versions.  A specific update to the twilio package required
some changes for how we determine the 'from' phone number. Also
alphabetized the packages in this file.  Finally, added the very
useful django-silk debugger/profiler.

simplejson package is used to properly serialize Decimal objects
(like gpstime) when converting from a dictionary to a json.

and email notifications. This is done by parsing
the label query separately and applying the filter
in a separate step.

as well as code to ingest the SimInspiral table and
a new template for injection-specific attributes.