Add instructions for developers.
Add shebang to gitzebo-repo utility.
Obey VIRTUAL_ENV variable if Apache sets it.

This clears a bug in Apache + mod_wsgi + venv deployments, where the
authorized_keys file sets the command to "None" as a result of not
being virtualenv aware.
Added password change warning to README.
Removes all default users other than 'admin' from initial schema data.
v0.0.7: Fixes broken authorized_keys when deployed in production.