From wagtail.utils
    Searches each app module for the specified submodule
    yields tuples of (app_name, module)

def get_app_submodules(submodule_name):
    """ From wagtail.utils
    Searches each app module for the specified submodule
    yields tuples of (app_name, module)
    """
    for name, module in get_app_modules():
        if module_has_submodule(module, submodule_name):
            yield name, import_module('%s.%s' % (name, submodule_name))