v1.6.0 partial prep - REVIEW

Improvements:
* support Django 1.5 and 1.6
* remove (some) DeprecationWarnings
* don't pin MPTT version
* Readme updates
* fix static files in dev environment
* fix incorrect package namespacing
* PEP8 formatting

New Features:
* provide reasonable default Section ordering
* 100% test coverage

Deprecating:
* remove Lettuce tests
* remove the Sphinx docs
* properly deprecate `find_related_models()`
* `SectionTreeAdminMixin`