Stack items withing groups change

Please see the changes after Dec 28th (*), the idea is to stack the items within a group. It is working pretty well, but I wanted to check I am on the right path for the changes to be included. A few notes:

- I also updated the examples
- currently the margins are bigger than the original timeline; they look better to me, but let me know what you think

If I have to do anything more, let me know.

Ste


(*) sorry, I am not very familiar with pull requests, I did not know how to select only those changes...