#15 jump "sections" when at edge of current section

[glenneroo]

page-flipping when border reached (if another section
to level exists)

e.g.

1
|
4 - 2 - 5
|
3

when in screen/map 1, going downward takes to
screen/map2 by "flipping" page rather than "scrolling"
screen continuously based on where tank is positioned.