Added Fabric tasks.

All my tasks run locally, but it'll be nice to be able to expand
with Fabric as my deployment needs get more complex.

Right now, I have tasks for each deployment action, and one combined
task, 'all', that runs them all.

They are:

    github:master - git push origin master
    github:develop - git push origin develop
    heroku - git push heroku master
    syncdb - heroku syncdb
    migrate - heroku migrate
    static_assets - django-admin.py collectstatic