Add virtualenv directory to gitignore
Run tests without requiring postgres.

This commit allows the use of sqlite3 as a backend for testing. To
test with sqlite3 simply do:

    export DB='sqlite'; python setup.py test

This also removes psycopg2 from the test_require list, and moves it as
an addition pre-test install for travis.
Remove django-celery dependency.
Added to contributors.
Merge pull request #26 from Wilduck/remove-djcelery-dependency

Remove djcelery dependency