Replace white spaces by underscores in example notebooks

Some example notebooks were renamed recently in d7d9b163, some of them now have white space in their name, which prevent them from being opened on gitlab.

This merge request suggests new names for these example notebooks, with "-" and "_".

assigned to @Petrush

Thanks! Forgot, we had this issue some years ago!

closed

(didn't see it was a merge request so did a rename from my checkin). Many thanks.

Thanks Petrus!