Fixed case where external user creates a log message with no
tags so that add_tag permission is not incorrectly required.

Switch over to new phone alert code (somewhat improved compared
to the old code).  Made a few more updates and bugfixes.

Removing old alert code in alerts.old_alert.  Finished migration
to new code by updating the phone stuff.

More informative error message when posting a log message from
the superevent detail web page.

We normally require permissions to add tags to log messages or to
create logs with tags attached, but we want to apply the
'analyst_comments' tag to log messages posted from the web form
no matter what, so we add a check where that doesn't require
special permission if the request is AJAX.

Fix "parent" object serialization for event alerts where the
"object" is also an event.  Now provide the subclass for
serialization rather than the base class.

Now require version 2.0.0 of the client and won't allow old
versions without the client header.

New unit tests which check what information is shown to different
user classes on the 'search' and 'latest' pages.

New unit tests which check whether different user classes can
access superevent detail pages and superevent file list pages,
and what information they are shown.

Better error handling for 'search' and 'latest' views.  Also added
filtering by user view permissions for the 'latest' view.

Fixed a bug in the mixin which handles whether to display the
EM advocate signoff form on the superevent detail page.

Small improvement to create_event mixin for unit tests.

Moved SupereventSetup to a mixin in the superevents app rather than
in a unit test file in the superevents API.

Moved request_as_user from GraceDbApiTestBase to GraceDbTestBase
so that it can be used in tests for other apps.

If an event is crated with labels attached, we issue 'label_added'
alerts as well.  The event is created, the 'new' alert is issued,
then each label is added and an alert is sent for each label.

Making signoff_type contents for superevent signoffs match that
of events.  Now use signoff_type codename instead of verbose form
in serialized object.

User documentation updated to include information about new
LVAlert contents and show serialized event, superevent, and
annotation objects.  Also an overall update of any missing or
outdated information.

New format for LVAlerts (XMPP alerts).  New class-based
functionality for issuing alerts for events and superevents.
See https://git.ligo.org/lscsoft/gracedb/issues/8.

Added a 'get_subclass' method to the Event model which is used to
get the CoincInspiralEvent, GrbEvent, etc. corresponding to that
Event.

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

Added a method to the Superevent model which returns a list of groups
who have group object permissions for that particular superevent.
Could be useful in the future.

It's too complex and doesn't make much sense to make the superevent
GOP serializer a group serializer, even though it makes the display
a bit nicer.  Instead, we view and serialize the GOPs themselves.

Moved context variables and calculations for determining whether
the confirm-as-gw form should be shown on the superevent detail
web page from the superevent detail view class to a separate mixin.

Updated the web view for the superevent file list to be a
class-based view which uses view permission-based filtering. Also
updated the file links on the list page to point to the file download
page on the API so as to reduce redundancy.  Removed the old file
list and detail web views.

Added some information about old/new IDs to the log message which
is created when a superevent is "upgraded" to a GW.

Moved some of the logic in the superevents file list API resource
to a function in the core app, so that it is more easily reusable
across the project.