RichText linkEventsHandled is broken

[jonathanolson]

It will never call handle(), and it's been this way for a while. I'll need to investigate the best and safest way to fix this. Discovered in phetsims/phet-core#103 (yay TypeScript)

The bug is:

self._linkEventsHandled && event.handle();

where self refers to window.self (and it's not even in RichText, so it's hard to forward that info over).