Added FIndCentroids notebook and a multiple channels ilastik notebook

[juliomateoslangerak]

Hi,

Here is what I did.

• There is an ilastik notebook very much like the previous one but working with multiple channels
• There is a python notebook that follows up on the ilastik notebook. It needs a bit of a better introduction to the goal of the analysis and some code beautification but it works very nicely. It is also a very common type of analysis.
  For the merge, do not take into account the Dockerfile changes. I just commented out some stuff to lighten the building. The only requirement that has to be taken into the python3 environment is scikit-image.
  I'll send a separate mail with further cosiderations about running this notebooks