Pages addon

Event needed for Page addon
@ForumHulp I just looked at your extension, and this event looks wrong. It looks like all you are doing with it is adding template vars. If that is true, then this is wrong. Why are you passing it `$content_for_edit`?

Looks to me like this whole event can be reduced, renamed and changed to:
```php
/**
* Event to add to Pages ACP add/edit pages
*
* @event phpbb.pages.acp_add_edit_page
* @since 1.0.0-RC1
*/
$phpbb_dispatcher->dispatch('phpbb.pages.acp_add_edit_page');
```