Paints block staple one line portion.
Overwrite DrawStaple to perform custom staple drawing.
X, Y1, Y2 - coordinates of staple vertical line;
Level indicates block staple level. First staple has level 0, second - level 1, ...
AFirstLine and ALastLine flags specify whether this part is on first or last line of stapled lines.
Staple - reference to staple object.