Limit editor to one screen size.

[ericbusboom]

When the user works on an editor, the editor can sometimes be much larger than the screen. You have to scroll down to the bottom of the code to hit the Run button and then scroll back up to see the turtle.

The editor should be limited to one screen size. The code should scroll up and down. When you hit the Run button, it should center the editor on the screen, or if you try to edit anything, it should center the whole editor on the screen and size it to be the size of the screen so that it is easier to see and use.