[cwctl] rewrite wsgi method choices This will help devs to add new choices by adding their callback to WSGI_CHOICES. Note: ``options`` becomes a property because ``wsgichoices()`` should be evaluated at the last-minute.

option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')