Move System::jsonExit to BaseModule->jsonExit

- This will ensure headers set in BaseModule->run will be carried in jsonExit scenarios
- Deprecate jsonExit() method in Core\System

src/Module/Api/Mastodon/Search.php

@@ -91,7 +91,7 @@ class Search extends BaseApi
 			$result['hashtags'] = self::searchHashtags($request['q'], $request['exclude_unreviewed'], $limit, $request['offset'], $this->parameters['version']);
 		}
 
-		System::jsonExit($result);
+		$this->jsonExit($result);
 	}
 
 	/**