[Gzz] Updatemanager thread

[Benja Fallenstein]

Hi Tuomas,

you've changed Gzz.py to use the updatemananger thread because it's 
required for OpenGL. But, the AWT client crashes before it starts again, 
now, saying: "Trying to add window; no updatemanager instance."

I don't know how to fix this except the way I did earlier: removing the 
Runnable stuff that runs in the other thread. I don't know why that 
helped it, but it did.

Please do fix soon!

- Benja