New Containment Breach gamemode

This is the gamemode where SCP validhunts you !

Since it's all brand new and fun, I'll just give a simple idea :

- SCP-173 is the main antagonist of this gamemode. For now. He'll most
likely stay this way, but more SCP/hostiles might be added
- SCP arrives via teleportation (near a vent, but hell). He immediately
triggers an EMP and a biohazard alert fires to rile up the crew (also,
this acts as a pretty malicious counter-metagame to Blob)
- After a few more minutes, SCP's presence is revealed. From there,
random events (justified by a takeover from SCP-079) run to make
everything much more complicated
- SCP-173 goes around fucking shit up. The goal is to get rid of him,
which is theorically done via teleporting
- If the crew is not done in a fair amount of time, both from SCP-173
wrecking shit and SCP-079's influence fucking up people, it (SCP-079)
breaches into the station's systems and arms the nuke Malfunction-style.
This is the loss condition

Further notes :

- There are comments for special announcement sounds. Uncomment then
after the announcements.txt file is generated
- This is a functional draft. Might see improvements and changes
- The goal is to make a gamemode that can pop up on Secret from time to
time. It might evolve into a more general spook round
- Yes, I know about the spawn() staircase. It has no effect on performance (IN THEORY), at worst it makes the code more annoying to browse
A weighted spawn will probably require reimplementing byond's weighted pick in softcode, 
Here's some example code for that:
```
/var/list/outcomes = list(
	"20"	= 1,
	"50"	= 2,
	"100"	= 3,
	"100"	= 4,
	"200"	= 5,
	"300"	= 6,
	)

/proc/pickWeighted(list/outcomes)
	var/slots[outcomes.len]
	slots += 0
	for(.=1,.<=outcomes.len,.++)
		slots += (text2num(outcomes[.]) + slots[.])
	var/ball = rand(0,slots[slots.len])
	for(.=1,.<=outcomes.len,.++)
		if(ball in slots[.] to slots[.+1])
			return outcomes[outcomes[.]]
	return null
```