More Mapping

Fixes #6913.
Splits the arrival section up into sub-areas to reduce the need of crew rescue when areas get breached.
Makes catwalks act as plating instead of floor.
Misc. changes.

Rough division:
![Sub-Arrivals](https://www.dropbox.com/s/q5j23beo9ixf7fm/SubArrivals.png?dl=1)
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