ControlRoomMiddleware is a new-style middleware, but that makes it
somewhat hard to unit test.  So we just split up the request and
response processing into separate functions which are called
within the __call__ function.

Remove several features from superevents detail pages for
unauthenticated users, since they wouldn't be able to use them
anyway: tagging/untagging log messages, adding log messages, and
adding EMObservations.

EMBB event logs seems to have been deprecated long ago (last
production instance created was April 2015) in favor of
EMObservations.  So we remove the corresponding view and tests.
Will preserve the table data for now, but it doesn't seem to be
useful.

Base test class for event permission testing where we create
events which are available to internal and LV-EM users. Also added
a utility mixin for exposing event logs to LV-EM, since
unfortunately, it's handled differently than for superevents for
the time being.

For the base test class which creates an LV-EM user and the
LV-EM observers group, we now also create the basic LV-EM group
and add the user to it as well.

URLs for editing contacts and notifications were defined, but the
view functions just returned 404 responses.  So what's the point
in having them at all?

A weird web view for processing GET (!) parameters and running
buildVOEvent exists in the events app.  I can't believe this is
still ever used and it should not be used in favor of the API.
So I am removing it!

Add django-user-sessions package for more easily managing sessions
and correlating them with user accounts.

Add/update tests of all web views in the superevents app for
public/unauthenticated access

Add/update tests of unauthenticated access to search web views

Now show 'Login' button if user is not authenticated.