Little things

Gave engine room airlock camera x-ray upgrade (so AI can see SMES).

Locked engine room core access doors.
Merge pull request #4350 from Loganbacca/dev-freeze

Minor mapping tweaks
Fixes #4355
Fixes #4346
Fixes #4306
Generalized yank_out_object().
Fixes #4223
Fixes #4219
Discovered/fixed a division by zero error for standing on the supermatter core.
Fixes #4089
Fixes #4195
Adding Kilakk's fix for #4145
Fixes #3907
Fixes #3847
Fixes #4107
Fixes #4078
Rogue comma, kill it.
Merge pull request #4357 from Zuhayr/master

Fixes
Merge branch 'master' of github.com:Baystation12/Baystation12 into dev-freeze

Conflicts:
	icons/mob/back.dmi
	icons/mob/mask.dmi
Merge branch 'dev-freeze' of github.com:Baystation12/Baystation12 into dev

Conflicts:
	code/modules/supermatter/supermatter.dm
	maps/tgstation2.dmm