'Get a project zone handler for the given project.
"proj" is an object representing the project. It should have
the following interface:
proj.path       path to project file
TODO: determine needed interface'

def get_proj_zone(self, proj):

    proj_path = proj.path
    proj_zone = self._proj_zone_from_proj_path.get(proj_path)
    if (proj_zone is None):
        proj_zone = ProjectZone(self.mgr, self, proj)
        self._proj_zone_from_proj_path[proj_path] = proj_zone
    return proj_zone
