[3.3.x] EditController: Fix item selection

Since iOS 13.0, forcing the cell's isSelected value to true is not enough for the collection view to allow the user to deselect a cell that has been initially selected.

Which was the case for the selected cells when the user decides to press the select all button.

The cells hidden by the collection view are now succesfully selected when pressing the select all button.

The select all button image is now updated when the user selects or deselects manually all the items in the collection view.