Add tables users, user_emails and use foreign key to link user to the users table

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Fix project's path and fullname now that we have a user table

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Fix the internal API to retrieve the correct user before creating/updating an object

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>