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/Smilies.php

@@ -41,7 +41,7 @@ class Smilies extends BaseModule
 			for ($i = 0; $i < count($smilies['texts']); $i++) {
 				$results[] = ['text' => $smilies['texts'][$i], 'icon' => $smilies['icons'][$i]];
 			}
-			System::jsonExit($results);
+			$this->jsonExit($results);
 		}
 	}