guf-show-demo: Initial addition of the guf-show-demo

Add the current rocko version of the guf-show-demo.
Currently does not work becasue of a shader issue:

```
QOpenGLShader::compile(Fragment): 0:7(2): error: No precision specified in this scope for type `float'
0:8(2): error: No precision specified in this scope for type `float'
...
```

Seems to be an issue with the OPENGL ES Default Precision Qualifiers
See also https://stackoverflow.com/a/56406788