Improve usability of facet filters screen to eliminate confusion around hook_facet_items_alter()

Problem/Motivation

The current filter settings form is confusing, leading multiple users to report alter hooks not working because of a missed duplicate checkbox. There are currently two checkboxes that have to both be checked for the hook to work, and yet they say the exact same thing and the second one is checked by default. Because of the layout of the page, the first one (unchecked by default) is frequently missed.

That second checkbox says "always checked" next to it, which doesn't make any sense in and of itself, but also distracts users away from the actual functional checkbox in the list above. WTF?

Proposed resolution

We should remove the second checkbox in the vertical tab and further have the first checkbox above the tabs use the states API to only show the tab below when the checkbox above is checked. Then, the vertical tab becomes merely an information pane, but I think that's fine, especially if it only shows when it's configured correctly to be meaningful.

Remaining tasks

Usability review and patch needed.

User interface changes

Modification to vertical tabs using states linked to filters checkboxes above.

API changes

None

Original report by johnish

hook_facet_items_alter() never fires. I have cleared cache and rebuilt the registry and the step through debugger still doesn't stop on it.

function veritas_facet_items_alter(&$build, &$settings) {
  if ($settings->facet == "my_facet_name") {
    $build[1]['#markup'] = t('My Custom Title');
  }
  if ($settings->facet == "item_details") {
    foreach($build as $key => $item) {
      $build[$key]["#markup"] = drupal_strtoupper($item["#markup"]);
    }
  }
}