Virology atmo tweak

This started as an attempt to solve the unwrenchable status of all the supply pipes in virology (tanks have no pressure regulation and as a result the whole supply section of virology would be well over 300Kpa).


After discussing it on IRC i basically tried to do several things with this modification:
-Improve (somewhat) the pipe layout in virology to have less pipes running under walls and furnitures.
-Connect virology to the main supply loop. (there is no reason not to).
-Replace the unmovable tank with a portable type (smaller, replaceable)
-Add a valve to isolate virology from the main loop if needed.
-Add a pump to control the pressure coming from the tank to still allow pipe work to be done eventually.

So what makes this setup interesting...
-Two way flow: which means that if virology wants to piggyback on the main atmo loop, they have to accept the pressure that supply give them, if atmo want to go wrench proof, it's how it's gonna be.
-Less autonomy/ Granted that it's very unlikely for the canister to ever drain, using a smaller model makes it more likely.
-You can potentially flood virology with something unexpected, so not using the atmo supply has it's risks.

Personally it's more in line with what i would expect from a realistic virus lab, even if it's just an "rp" element.

Now for pictures:
![image](https://f.cloud.github.com/assets/598409/1514830/d5f24088-4af8-11e3-9084-9cf73c06134c.png)
Due to the cramped state of the maintenance area here, this was the only possible place for the canister, and putting it south would have required a long line in a wall. There is no connection with the scrubber line, i checked.
I ran the supply line through the airlock instead of south to avoid the wall or going under the smartfridge. The pump is off by default and the valve to main supply line is open. They are both labeled.