Update findHooks.php and move MonoBook hook out of docs/hooks.txt

Added includes/skins/ to the list of directories and removed
the skins that were moved out of core.

The MonoBook hook is moved to skins/MonoBook in Ieb85b4bed.

Change-Id: Ie8ad1eb694575b8e1485177e2d14f2a9dcab179d