improve copy/paste behavior, also multi-row selection

Hi, working with hypergrid, to achieve a more complete copy/paste behavior and better user experience, I got some questions or proposals. Any answer about how to implement them elegantly would be very helpful. And if there wasn't be implemented, I'd like to help.

1. multi-row selection
Selections and especially multi-cells selection to me is designed to work for copying. Now hypergrid supports cell range selection(including all cells), multi-columns selection, and single-row selection.

I think multi-rows selection should be supported as well, which can behave as same as columns selection--dragmove, ctrl, shift, etc.(tick toggle can be used as well)

workaround: none?

2. copy header and fix column header copy
Now, there are only two ways to copy including header--all cells & column-wise selection, and no way to copy header alone. It seems no suitable operation to select header, single click selection the whole column and double click may trigger sort.

Even when header was selected, they are not treated as header cell, and caused a `undefined` text transformation bug.

workaround: overriding copy event listener?

3. paste into grid
Paste, or `Ctrl` `+ `V` is not handled by grid. Is there any concerns for adding this feature?

workaround: write a listener to handle `ctrl + v` and modify the cells