Improve pointcloud visualization with colormaps

[aecins]

Currently PointCloudColorHandlerGenericField allows visualizing pointclouds colored based on one of it's fields using the default VTK colormap . It would be useful to add the following functionality to PCL:

• Introduce several colormaps (JET, HSV, GRAY, BLUE2RED)
• Add API to change the colormap used to color a cloud
• Add API to change the minmax values of the LUTs used to color displayed clouds
• Add a ColorHandler that allows coloring points based on generic data (i.e. a vector of floats)

I am looking into how this can be done. I have seen that this issue has been addressed for meshes (#1143, #1241), but not for pointclouds.

[aecins]

Closed by #1581.