A Message extends the meaning of an ACLMessage (thus extending
jade.lang.acl.ACLMessage) providing an ACLMessage with the graphic part: the
arrow going from the sender of the message to the receiver of the message to
be drawn on the Message Canvas
This method is invoked every time a user double-click on a blue arrow in the message canvas: the double-click occurs
on a blue arrow in the message canavs, a dialog box is displayed with the entire
message.
Makes the two canvas.One is the agent canvas which is useful
for drawing the agent's box and other is the message canvas
which useful for drawing the message with blue arrows.