Spreadsheet selection model

I've few things to spreadsheet selection model:

- rownumberer should have header behaviour - copy paste, selection etc should be ignored on this column + rownumberer should have same background color as header

- when you use arrow + shift selection you should jump stop in the last column - currently you select 2 rows - one where you are and the one below

- I've found two spots where you create rownumberer (this should be definitely changed to private function)

Spreadsheet selection model