Make server listing and single server view API endpoints work

app/Transformers/Api/Application/ServerVariableTransformer.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Pterodactyl\Transformers\Api\Application;
+
+use Pterodactyl\Models\ServerVariable;
+use Pterodactyl\Services\Acl\Api\AdminAcl;
+
+class ServerVariableTransformer extends BaseTransformer
+{
+    /**
+     * List of resources that can be included.
+     *
+     * @var array
+     */
+    protected $availableIncludes = ['parent'];
+
+    /**
+     * Return a generic transformed server variable array.
+     *
+     * @param \Pterodactyl\Models\ServerVariable $variable
+     * @return array
+     */
+    public function transform(ServerVariable $variable)
+    {
+        return $variable->toArray();
+    }
+
+    /**
+     * Return the parent service variable data.
+     *
+     * @param \Pterodactyl\Models\ServerVariable $variable
+     * @return \League\Fractal\Resource\Item|\League\Fractal\Resource\NullResource
+     */
+    public function includeParent(ServerVariable $variable)
+    {
+        if (! $this->authorize(AdminAcl::RESOURCE_EGGS)) {
+            return $this->null();
+        }
+
+        $variable->loadMissing('variable');
+
+        return $this->item($variable->getRelation('variable'), $this->makeTransformer(EggVariableTransformer::class), 'variable');
+    }
+}