#2 recenter robot on canvas

[Stas Zytkiewicz]

(This was also reported as a bug, stas)
If the robot moves off of the visible screen, the
screen does not recenter onto the robot.

Example: The width of the screen is 14 streets. If the
robot is at the 13th street and moves 5 times (while
facing right) the screen will not move to be able to
see the robot as it moves beyond the 14th street.

[Stas Zytkiewicz]

I started a rewrite of the frontend so this bug is not relevant anymore