CellSelection subtraction

[JimKnoxx]

Hi!
Thank you for adding cell selection state management!

Currently multi selection is only additive. Can you also add support for subtraction?

In concept:

• Holding the "multi select key" while clicking on a selected cell deselects the cell
• Holding the "multi select key" while dragging from a selected cell deselects the cell and all other selected cells in the new selection area. Unselected cells stay unselected.
• Holding the "multi select key" while dragging from a unselected cell selects the cell and all other unselected cells in the new selection area (current behavior). Selected cells stay selected.

With "multi select key" I reference the cmd key on macOS.

With this I could "correct" my selection easily, for example "All cells, but not these 5 in row 2".

[KevinVandy]

Coming soon...