Add passingt est for adding a Term to an Item
Add unicode methods for Taxonomy and Term
Change the unique contstraints for Term so that
Term name needs be unique only for a given Taxonomy

Removed taxonomy and term classes from data_layer - just reference the ones
in taxonomies app directly for now.

Will need to run "deploy/tasks.py clean_db" and "deploy/tasks.py update_db"

Ive been working through some options for how the REST
api will work with categories in the readme file.

The last error from running the tests was that the TErm table didnt
exist in the test database. So I'm running

    manage.py makemigrations

And it fails with

    AttributeError: 'NoneType' object has no attribute 'unique'

Following the [django docs](https://docs.djangoproject.com/en/1.8/topics/db/models/#abstract-related-name)
I put in:

        related_name="%(app_label)s_%(class)s_term"

But still can't even get a helpful error message.