update migration to the output from a newer South (0.8.4)

There's nothing here that changes our practice as South supports Django 1.2+. Unicode can't hurt and `db_index` on SlugField has been implied since Django 1.2 (maybe earlier).
use future/now-current version of `{% url %}` in template
Deprecate the `SectionTreeAdminMix`. It's better `mptt` practice to use TreeForeignKey/TreeOneToOneField/TreeManyToManyField explicitly in the model definition.

- I don't believe we've ever used this in Armstrong itself so I don't think there is anything else to change.
- drop EMPTY_LABEL. It doesn't appear necessary.
- Fix: using EMPTY_LABEL in `formfield_for_manytomany()` was actually breaking
development env - fix static files use in newer Django's and provide required `STATIC_ROOT` setting. Drop Sites. Add some "no covers" for Coverage.
Coverage - increased to 100%. Fix duplicate test case name.