Simplify migration between event names

We have some misspelled event names and it might be worth it to have an easy syntax in which we can give extension authors time to migrate to the correct event to not break backwards compatibility.

This might also be helpful when moving some front-end pages to the controllers to have some names which fit to the naming scheme. (Or maybe we have two events now which will do practically the same in a later version..)

For all these reasons there should be an easy syntax but fear not! Thanks to the new array syntax introduced in PHP 5.4 we can have something as easy as:

$dispatcher->trigger_event(['new_name', 'old_name'], $vars);