Protect sequences provided or generated for the default value of ``MenusField`` from being forced to unicode (as for example u'[1, 2, 3]').
Django forces fields defaults to unicode unless they're callable (see ``Field.get_default``). This is done to prevent problems that could arise from setting the same mutable object as a default for many fields (see Django ticket #18478).
Database-prepare tuples in the same way lists are handled in ``MultiChoiceField``.
Pep8, blank lines before inner classes.