Update ``Hub`` models to match updated definition.

https://github.com/madewithbytes/us_ignite/issues/169

The models have been amended to match the updated definition.
Amend the ``Hub`` admin section.

https://github.com/madewithbytes/us_ignite/issues/169

Make sure that the updated models work in the admin
section.
Update ``Hub`` views to use the ``contact`` user field.

https://github.com/madewithbytes/us_ignite/issues/169

The ``Hub`` ``guardian`` field has been replaced by a
``contact`` field. This selected user can modify
the details of the ``Hub``.
List the managed ``Hubs`` in the ``User`` profile.

https://github.com/madewithbytes/us_ignite/issues/169

The hubs where the user is the ``contact`` are listed
in the profile.
Update dummy content generator to match ``Hub`` definition.

https://github.com/madewithbytes/us_ignite/issues/169
Set cascade null on the ``Organizations`` in the ``Resources``.

When an organization is removed make sure
that the Foreign key is set to null instead of
removing the object.