Django 1.7 and misc. fixes

* Initialize django during tests to prevent app loading issue
* Reorganize test imports
* Fix make (test, coverage, release) commands
* Add `htmlcov/` directory to .gitignore
Expand travis build matrix

* Test python 2.6 & 2.7
* Test django 1.4, 1.6, 1.7
Only test on Python 2.7
Merge pull request #17 from mwarkentin/django-1.7

Django 1.7