New /latest/ page includes events and superevents. We also
move the old events 'latest' page to /events/latest/, changed the
view name, and fixed reverses to that page appropriately.

Modified events.view_utils.reverse to return an absolute url using
core.urls.build_absolute_uri.  This is helpful for when we issue
alerts without a request object available to construct the absolute
url.  Also updated the corresponding *toDict methods so as to
take advantage of this.

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.

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.

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.