udl: install udl add-ons into the distributions folder
https://bugs.activestate.com/show_bug.cgi?id=96295
* while some of these add-ons could be uninstalled, they clog up the
  add-ons UI and disabling them has minimal performance impact

(integrated from trunk branch change fa97b97 by Todd Whiteman <toddw@activestate.com>)