Flesh out the app path in /opt

Looks a little something like this:
/opt/<app-name>/shared/log   - I think this should link to
/var/log/<app-name>
                      /venv  - Virtualenv directory
               /releases
Add a run-procfile script and call from upstart
Create pip download cache directory
Merge pull request #5 from alphagov/flesh-out-app-directory-2

Flesh out app directory 2