Add system checks to applications

See merge request !10

add django 2.1 support

No code changes but update our requirements and travis configuration to
include Django 2.1.

add missing migration

The user field in UserLookup had on_delete modified but this had not
been reflected with a new migration. Add it.

Add a convenience "makemigrations" env which allows running the
makemigrations.py script with the appropriate packages installed.

The makemigrations.py script did not pass its arguments to the
underlying management command which made it difficult to set the name of
a migration.

While there, update the list of installed apps in the "micro settings".

Decouple lookup and OAuth2 token authentication

The lookup functionality was too opinionated in how it was to be coupled
with the DRF authentication which lead to a problem in the Media
Platform whereby users which were created by being simple Django users
ended up with the wrong scheme somehow.

The fix for this is to decouple the Django user creation from the lookup
calls. Unfortunately, since it was copied wholesale from the IAR
project, the implementation of automationoauthclient, automationlookup
and automationoauthdrf was very tightly coupled.

Taking the lead from #4, move OAuth2 client functionality into a new
automationoauth module and factor out the token verification from
automationoauthdrf into automationoauthclient.token.

Do not remove the existing implementation for compatibility reasons but
re-implement it with the new API. Improve the documentation for the new
API a little and mark the previous API as deprecated.

Do not couple the OAuth2 token subject to the lookup proxy API since, as
in the UMP, we do not always have an OAuth2 token for a user we wish to
look up and so cannot rely on the automagic parsing of the token
subject.

Port fix to tox coverage reporting.

Test Djangos 1.11 and 2.0 in Pythons 3.4 to 3.6. Run flake8 & build docs
in Python 3.6. Deploy documentation when built.

Tweak the default env list to check only supported combinations of
Python version and Django.

removed test requirement for python 2.7 and django 1.8

by interacting with the LOOKUP and OAUTH service.