CellTracksColab_TrackMate.ipynb: Creating the output folder

[m-albert]

Hi CellTracksColab team, I was just trying out the above notebook as part of the Pasteur NEUBIAS course led by Laura and Joanna!

I stumbled upon a problem when using it with the test data downloaded by the notebook: When not changing any setting in the "Provide the path to your dataset:" cell, it throws an error because it doesn't create the output folder by itself. Perhaps it would make sense to either create it automatically or remind the user to create the output folder themselves.

Thanks!