They just need to register to the PLUGIN_USAGE_DATA event, and then to add
either a simple string, or an array of key / value. For example:

    function register(Doku_Event_Handler $controller) {
      $controller->register_hook('PLUGIN_USAGE_DATA', 'AFTER', $this, 'usage_data');
    }

    function usage_data(&$event){
      $event->data['my_plugin_name'] = 'my usage data';

      //or: $event->data['my_plugin_name'] = array ('k1' => 'v1', 'k2' => 'v2');
    }

- replace PHP4 style class constructor function names (based on
  class name) with php 5 __construct()
Also remove some '&' reference operators used with objects
And add some object type hints

removed </a>

It is helpful if the pipe is still inserted by the linkwizard when there
is no title. This increases usability for beginners.

The viewing options should only be visible on the first tab - which is
the installed Plugins tab. (There seems to be no more direct way to
address this tab.)

This reverts commit 3940c519 as
discussed in #1082.

Since it is a JS function only, the form will be generated by it too.

Allows tho show/hide extensions that are: enabled, disabled, updatable