Allow listeners to receive only events from their own namespace

Steps to reproduce

• In a subwiki, create a WikIComponent listener with scope "current wiki" as described in the EventListener tutorial
• Make sure that the listener works as expected by editing and saving a page of the current wiki: some extra content gets added to it by the listener.
• In a distinct subwiki, edit and save a page.

Actual behaviour

The page that was updated in the other wiki gets some extra content as well, which is not expected when the WikiComponent scope is set to "current wiki".