Pass menubar preference as a param. Simplify cache mechanics. (#8)

Ex: If an admin uses an API call (CLI/REST) to change the menubar color,
then they don't need to follow-up with a cache-clear.  The new setting just
goes live.

Ex: If a customization (via `civicrm.settings.php` or via extension) decides
on the color scheme programmatically (e.g.  per-domain or per-role or
per-user-preference), then they don't need to clear cache.  Multiple color
schemes can coexist.

CRM/Admin/Form/Preferences/Display.php

@@ -106,8 +106,6 @@ public function postProcess() {
 
     $this->postProcessCommon();
 
-    \Civi::service('asset_builder')->clear();
-
     // If "Configure CKEditor" button was clicked
     if (!empty($this->_params['ckeditor_config'])) {
       // Suppress the "Saved" status message and redirect to the CKEditor Config page

CRM/Core/Resources.php

@@ -765,7 +765,9 @@ public function coreResourceList($region) {
       $items[] = 'bower_components/smartmenus/dist/jquery.smartmenus.min.js';
       $items[] = 'bower_components/smartmenus/dist/addons/keyboard/jquery.smartmenus.keyboard.min.js';
       $items[] = 'js/crm.menubar.js';
-      $items[] = Civi::service('asset_builder')->getUrl('crm-menubar.css');
+      $items[] = Civi::service('asset_builder')->getUrl('crm-menubar.css', [
+        'color' => Civi::settings()->get('menubar_color'),
+      ]);
       $items[] = [
         'menubar' => [
           'position' => $position,
@@ -844,7 +846,7 @@ public static function renderMenubarStylesheet(GenericHookEvent $e) {
     foreach ($items as $item) {
       $e->content .= file_get_contents(self::singleton()->getPath('civicrm', $item));
     }
-    $color = Civi::settings()->get('menubar_color');
+    $color = $e->params['color'];
     if (!CRM_Utils_Rule::color($color)) {
       $color = Civi::settings()->getDefault('menubar_color');
     }