minor
Fix chapter div width

When `#editorPane` is displayed then half of `#chapter` element was overlapped under `#editorPane` because of `width=100%`.

Set its width to absolute value 600 (canvas width) + 2 + 2 (canvas left and right paddings) = 604px.
Absolute values are acceptable now due to `canvas` size is also absolute.
Merge pull request #303 from phts/fix-chapter-div-width

Fix chapter div width
better approach to fixing chapter alignment
adding levels from hangoverx
adding hangoverx levels
adding three new bonus levels from paulcdejean and mdejean
slightly more challenging DOM level (better late than never)
oops, that part was unnecessary:
bump lvl19 to 1.3
Update 12_robotNav.md
Merge pull request #304 from ToeFungi/patch-1

Update 12_robotNav.md