Allow Visualizing extra Data

[Robert42]

• [x] node editor
• [x] applying shader
• [x] test combobox behavior
  • [x] applying a shader should update the combobox value
  • [x] loading a pointcloud incompatible to the current shader should not be a problem (as the combobox is loaded tro the default value)
  • [x] test switching the combobox to a not supported shader
• [x] test saving/loading shaders ...
  • [x] ... in ini files
  • [x] ... in pcvd files files
• [x] allow renaming the sahder
• [ ] store all shaders with the settings?
• [ ] add more nodes
  • [ ] Interpret data as discrete class -> distinct color per class
  • [ ] Add Gradient for values
  • [ ] show normals color coded