Added all the game options except for Air Control and Grappling Hook... the air contr...

Added all the game options except for Air Control and Grappling Hook... the air control was confusing because there already seems to be such air control :) I could rewrite or clean out the sv_user.qc physics file if you want.
Instagib, Strength Gain on kill, fast health regeneration, rocket arena, no self damage, low gravity, and fullbright players are all implemented. The value is read from the 'gamecfg' cvar on level load. Look at constant.qc to see the bitflag values for each game option.
A few notes:
- I don't know what to do with health or armour items in gametypes such as instagib and rocket-arena. Should they be removed, like the weapons and ammo are?
- There didn't seem to be any powerup code. I added the entity fields required for them so I could get the strength powerup on kill thing working. Although, it doesn't work, because strength powerup does nothing :) I might look at this soon.

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@192 f962a42d-fe04-0410-a3ab-8c8b0445ebaa