Add new user roles: World Writer and World Editor

NOTE: These will need to be added to sign-on-o-tr-o-n.
Add tests for what world writers and editors can do to normal editions
World writers and editors can't do anything with Fatality Notices
Added rules for WorldLocationNewsArticles

Flips the situation with world editor/writers and dept editor/writers when it comes to edition permissions.  Only world folk can do things to world location news articles and dept folk can't.  Still respects the location of the object.  GDS Editors still have full permissions.
Reduce duplication somewhat in authority_test_helper
Reduce duplication in fake classes defined in authority_test_helper
Move the generic bit of authority_test_helper to the top
Add permissions tests for worldwide priorities

They follow the same pattern as world location news articles, so we move WorldLocationNewsArticleRules to WorldEdition and make both WorldLocationNewsArticle and WorldwidePriority use this as their rule set.