Introduce a user right for voting in non-contests

Currently it is only possible to restrict who can vote in contests, there is no way to do this for the "general" page rating. We could implement a user right for this purpose and give it by default to *.

Original feature request: https://www.mediawiki.org/w/index.php?title=Topic:W6z9mlxzbrklm6sw&topic_showPostId=w709z8w5mx34u17z#flow-post-w709z8w5mx34u17z