Improve the JavaScript API

Although the old code was a bit much, the 6.x-1.x version of the module did some interesting things with JS that we should revisit and rework into something simpler.

One item that might make JS code more reusable and prevent widgets from having to loop through all of the settings to find out which ones it should act on would be to implement a "callbacks" key for $this->jsSettings. The code would look something like this...

// For the "links" widget...
$this->jsSettings['callbacks'] = array(
  'Drupal.facetapi.applyLimit',
);

// For the "checkboxes" widget...
$this->jsSettings['callbacks'] = array(
  'Drupal.facetapi.makeCheckboxes',
  'Drupal.facetapi.applyLimit',
);

See comments starting at http://drupal.org/node/1175718#comment-4564222 for more details.

Marking as postponed. This seems like it would be better suited for the 2.x branch.

Moving to the 2.x branch.