Fix #7174

Closes #7174

Adjusts the truncation in the notebook for multiindex dfs. Both rows and columns are affected. 

Unfortunately, getting truncation to work with multiindex is a little tricky. At the moment some issues remain (see below). Number two might have to wait. 

Todo: 
1) The problems reported in 7174 are fixed but there are still some cases where the behavior is strange. 
2) So far I have not tested how this plays out with multi indices with more than 2 levels.