Virtual member functions

• virtual void reset(void) - resets the user interface to the initial state it was in when it was created.
• virtual int act_on_command(int, Commmand *, int) - this is called each time a Command is executed that the Mouse has expressed interest in hearing about. This will be when a mouse event occurs, such as a mouse button press.
• virtual int check_event(void) - calls the necessary routines in DisplayDevice to determine if a button has been pressed. If not, then any angular velocity is used to rotate the current scene.