save category bundles in variable_set so that on module uninstall those bundles and the fields attached to them get deleted .
this allows enabling the module after uninstall without field attach colliding with pre-existent field data entries .
http://drupal.org/node/1924532
attaching user_category view modes to the user entity modes
this way if someone does user_view($user, 'client') it will be passed on to user_categories_category_view
and site builder can configure field display using field ui for the user_category entities