Allow image data to be shown with colormaps

The image data is now greyscale. Being able to show it in e.g. Viridis would be nice. We should consider making it possible to create a colorbar in this case.

There are different ways to implement this. Ranging from leveraging numb, scikit-image, or Pillow. One very interesting approach is to produce paletted PNG's, with the palette being the colormap. This can be done via e.g. Pillow or pypng. 

