ENH: allow concat of Styler objects
  - [x] closes #43875
  - [x] closes #43894 


![Screenshot 2022-02-23 at 21 12 16](https://user-images.githubusercontent.com/24256554/155400528-fd512767-c303-4724-8c59-ab6fb6169cdc.png)
![Screenshot 2022-02-23 at 21 12 23](https://user-images.githubusercontent.com/24256554/155400535-c980193d-78a7-4147-92b9-1ac2cf403f08.png)


Not sure if this assessment is correct, but this would this be a generic version of `pd.pivot_table` + styling? 
https://pandas.pydata.org/docs/reference/api/pandas.pivot_table.html > only a very brief look but the same problem as the other PR this is commingling calculation and display

yes, ok i now see your point. how about I change tack and require a user to pass an already calculated dataframe or Styler object which will be appended to the footer? This would also get around any need to format or style the footer since it would inherit from the passed Styler object? @jreback I completely reworked this and managed to get the entire implementation under 20 lines execution code. All calculations are done by the user, they just pass a second styler object.