simplify default for addHook

[ayurmedia]

$this is already known and no need to pass as parameter

[romaninsh]

wrong place to raise commend, but this won't always, work, because in most casse you have 2 objects in the work here:

$obj1->addHook('hook', $obj2);

this way $obj1 will call method of $obj2. Adding hooks on the same object is actually a rare case.