Package update to `django-mptt`. Resolve DeprecationWarning by explicitly defining a TreeManager.
Order tree nodes by `title` and also provide a default ordering for non-TreeManagers (like `objects`).
SectionManager orders the same as TreeManager
Remove default ordering. SectionManager provides the ordering we expect and this Meta block is a confusing alternative.
remove explicit Django `install_requires` in setup.py. remove deprecation warning in Django 1.5 for url imports.
Merge pull request #22 from joncotton/ordering

Provide reasonable default ordering for Sections. Small updates resolving DeprecationWarnings, part of Django 1.5 preparedness.