Description of the new feature/enhancement

It would be nice to have a FPS overlay to indicate the current rendering FPS. You've all seen this in various kinds of games. I'm confident that this will not be the craziest feature request for the WT project.

Proposed technical implementation details (optional)

Well technically the FPS is quite easy to calculate, the overlay might be a little bit trickier, depending on what information we need to display and how to display them.