Vox skipjack now filled with nitrogen

Added an oxygen canister, breathmasks and tanks for "guests," thought I
don't think they will be needed since people rarely get to the skipjack
without internals of their own.
Added second vent to skipjack airlocks

Hopefully this will encourage players to not just force the airlock
doors every single time.
Adds a few backpacks to starboard maintenance
Merge remote-tracking branch 'upstream/dev' into vox-skipjack
Fixes missing phoron/plasma canister
Merge pull request #5114 from mwerezak/vox-skipjack

A few vox skipjack related changes