use the ‘pubsub’ class as a means to tag DOM elements that need to receive API events

use the ‘pubsub’ class as a means to tag DOM elements that need to receive API events
this is instead of the ‘plugin’ class that was used previously, and that relied on the
DOM building helpers and conventions that we have in place for ‘real’ plugins
However we want to be able to deal with plugins that piggyback on existing DOM elts
that do not necessarily have .plugin
As a side effect the topmenu buttons do not need to have .plugin to work with validatebutton