Sherpa Prototype

For ASSIGN & BLANK it's just one number stored inside property lines[0].
For IF & LOOP the same property stores the lines numbers of each line used to represent the syntax elements of a given statement, e.g. lines[0] holds the line for the IF, lines[1] the line for the THEN, lines[2] the line for the ELSE, lines[3] the line number for the ENDIF.
This allows to locate the first & last lines of an entire statement in order to add the "SelectedLines" marker to it.
This is done after having a onclick handler go recursively through the statements to mark their selected property to be the opposite of the selected property of the statement we just mouse-downed on