FEATURE #1373: add history of content

This commit contains only core funcionality of displaying history. Module settings must be implemented in each module.

app/Handlers/Handler.php

@@ -1,28 +1,23 @@
 <?php
 namespace App\Handlers;
 
-use App\Models\Content;
+use App\Handlers\Contracts\AppHandler;
 use App\Models\User;
-use Illuminate\Support\Facades\Auth;
 
 /**
  * Class Handler
  *
- * Handler is a class which handles module-specific behaviour which cannot be done by module itself, resp. cannot be done by some abstract magic.
+ * Handler is a class which handles module-specific behaviour which cannot be done by module itself, resp. cannot be
+ * done by some abstract magic.
  *
  * @package App\Handlers
  */
-abstract class Handler
+abstract class Handler implements AppHandler
 {
-    /**
-     * Render given module into visitor area.
-     *
-     * @param Content $content    DB model from table contents
-     * @param array   $parameters parameters used for modifications/custom settings of given model
-     *
-     * @return mixed
-     */
-    abstract public function render(Content $content, $parameters);
+    public static function getHistoryHandler()
+    {
+        return History::class;
+    }
 
     /**
      * Register admin menu (or multiple ones)
@@ -34,6 +29,6 @@ abstract class Handler
      */
     public static function registerAdminMenu(User $user)
     {
-        //
+        // core menu is registered in AdminMenuServiceProvider
     }
 }