Quest Complete, FindCreature, OnLevelChanged

Adds FindCreature that is declared but not defined yet.

Changes the comments on OnLevelChanged hook from newlevel to oldlevel (was really confusing..) and saying the hook was called before leveling to after.
Since the hook is called after, you should be able to get the new level with GetLevel if needed, so its not needed in the hook.

Fixes the Quest Complete hook. A script already seems to use it, but it is never called.
Not exactly sure about this, but this is how the other hooks are coded it seems.