capture number of lines deleted when there is a selection

only for when a key is typed replacing the selection or when the
selection is deleted by the delete or backspace key commands

the code determines if the selection contained multiple lines and
reports these lines as deleted, except for the first line, which is
marked as modified and will be reported as changed once the cursor
leaves this line

a new Selection class was implemented to capture the selection
a new slot was implemented to capture and save the number of characters
  removed and added
a new function was implemented to capture any lines that were deleted
  when there was a selection before a key was entered and emit them