2012-07-29 itemtype followups
shorter names for modify_show_*_selection.html templates - pull request accepted
allow +show to be overridden by itemtypes; (currently only +modify is) - needed by BOTH ticket system and blog - codereview: http://codereview.appspot.com/6457048
restructure registry code to reduce boilerplate - codereview: http://codereview.appspot.com/6453060/#ps1