Move System::httpExit to BaseModule->httpExit

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

src/App/Page.php

@@ -496,7 +496,9 @@ class Page implements ArrayAccess
 			}
 
 			if ($_GET["mode"] == "raw") {
-				System::httpExit(substr($target->saveHTML(), 6, -8), Response::TYPE_HTML);
+				$response->withBody(Utils::streamFor($target->saveHTML()));
+				System::echoResponse($response);
+				System::exit();
 			}
 		}