Added custom Django Admin, Fix issue 17, other elements

[marianoeramirez]

In this pull request, I did some changes to your awesome project.

1. I added a custom Django Admin model, now the action to import the data it's only visible on the admins that inherit from ImportActionModelAdmin, Probably I have to add this information to the documentation if you agree with this change I will add this to the documentation
2. I changed some import options to be relatives
3. Added a check data_wizard/tasks.py to see if the user is not None.
4. Changed the reverse URL on data_wizard/views.py, to work with Django URLs
5. Fixed issue Element a tag is not closed #17

[sheppard]

Thanks, this is a useful set of changes. I merged this after making some small adjustments to get it working in a couple of the test environments.

Feel free to submit a separate pull request to update the documentation.