A strategy for selecting figures when using the SelectAreaTracker. You can
implement a non-default strategy in order to control which figures are
selected when rubber band selecting. One example is in board games where you
may select a set of checkers but this strategy can remove opponent checkers
so a selection operation only select your own.
Add figures in 'model' to the model's internal selection. The figures that
are added to the selection is controlled by the 'rubberBandRectangle' (the
rubber band the user has dragged in the view) and the toggle.
PostCondition: model's selection is updated with the figures within the
rubber rectangle (or what ever the strategy decides).
model - the drawing where figures should be selected in
rubberBandRectangle - the rectangle selected
toggle - if true then figures are not added but "toggled" in and out of the