Vector: Move 'editwarning' feature from Vector extension

* Created a new Resource Loader module
* Created an entry for the RL module in the Resources.php
* Added messages to languages/MessagesEn.php and languages/MessagesQqq.php
* Called the new RL module from the EditPage.php
* Added required entries in the messages.inc, DefaultSettings.php

Corresponding change in the Vector extension: I164f17255bc927

Bug: 46514
Change-Id: I7bdbd09f4083ccb316156307400ccfacdfec79e1