Add form to edit a ``Hub``.

https://github.com/madewithbytes/us_ignite/issues/97

The Hubs will be edited by the guardian.
Add edit ``Hub`` mechanics for user guardian.

https://github.com/madewithbytes/us_ignite/issues/97

The guardian of a ``Hub`` will have access to edit
the hub details.

The changes are updated via a ``ModelForm``.
Add link to edit an Ignite community.

https://github.com/madewithbytes/us_ignite/issues/97

Only the ``guardian`` of a community will be able to see and
edit the ``Hub``.

The edit form can be accessed from the detail page of
a community.