Print text in console triggering graphic updates at the wrong moment

[BrunoLevy]

The mechanism that redraws graphics whenever the console has something to display needs to be protected by a lock.
It has problems with the following circumstances:

• When a function called from a mouse handler displays something in the console, see the following PRs:
  • Clicking on GUI elements picks 3D mesh elements under them. GraphiteThree#25
  • Probe tool sometimes keeps popup open after mouse button is released. GraphiteThree#26
• When a thread displays someting in the console (@PlathC)