Syndicate Strike Team and Deathsquad Improvements

- SST and DS members now get advanced magboots instead of combat boots,
with the SST getting ones that share a sprite with the blood-red
magboots.
- SST and DS members now get a fully pressurized double emergency oxygen
tank, as the emergency oxygen tanks they were getting were laughably
inadequate.
- Filled double emergency oxygen tank is a subtype of the 1/3 filled
one, so those are left unchanged.
- SST space suits are now as armored and acid-proof as DS space suits.
- SST space suits are now a subtype of the two specific colored
Syndicate spacesuits they used, so the originals remain unchanged, as
they spawn on away missions.

code/game/objects/items/weapons/tanks/tank_types.dm

@@ -174,6 +174,16 @@
 	icon_state = "emergency_double"
 	volume = 10
 
+/obj/item/weapon/tank/emergency_oxygen/double/full
+	name = "pressurized double emergency oxygen tank"
+	desc = "Used for \"emergencies,\" it actually contains a fair amount of oxygen."
+
+	New()
+		..()
+		src.air_contents.oxygen = (10*ONE_ATMOSPHERE)*volume/(R_IDEAL_GAS_EQUATION*T20C)
+		src.air_contents.update_values()
+		return
+
 /*
  * Nitrogen
  */