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.

Updated event static file serving to use X-Sendfile with Apache.
This is faster, more efficient, and seems to resolve the issue
with FITS file downloads from the web browser:
https://bugs.ligo.org/redmine/issues/6194

Added requirement that event.search is not None before checking
that event.search.name is MDC.  Fixes a bug which occurred when a user
tried to get an event by specifying 'M1234' when the event was not
an MDC event (and didn't have a search associated with it).

Missed one case where 'tag' should have been 'tags' in
58efeab3. Also updated same thing
in documentation.

Fixing issue where some float fields were left as strings in
LVAlert JSONs and response JSONs.  Occurred because they were
extracted as strings from files and saving the event did not
fix the attribute types without refreshing from the database.
See https://git.ligo.org/lscsoft/gracedb/issues/10.

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

Event time nanoseconds did not include leading zeros when printed
in event.log (since 2010!!). See
https://git.ligo.org/lscsoft/gracedb/issues/9.

adding optional override to Event delete() method which removes data directory and all associated GroupObjectPermission objects