Fixed an issue which could have caused the FPS to stop updating.

The issue was that the resolution of the getRealTime values was so bad,
that it couldn't be used on all PCs for checkin when enough time has
elapsed.

This patch also changes it back to updating each frame for the following
reasons:

- The FPS number is already an average so usually the value doesn't change
  by much.
- Any large FPS changes should be eliminated by us in the long run
   -> there should be no spikes
- You can see the results of what you do instantly
   -> you don't need to wait for a half second
- You don't miss performance drops that occured only at a few frames
- If the numbers update so slowly it looks like the game is having
  issues to update the UI
Merge PR #1382 by @flo - FPS display fix