Changes

Added 3 Parameters to SmokeScreen
Performance seems unimpacted, tested locally, should work fine.
randConeEmit - Default value 0 (no cone emission), similar to 
randomInitalVelocityOffsetMaxRadius, but a little less random effect 
appearance in-game.  Forces a mirrored emission to ensure symmetric 
plume appearance.
xyForce - default value 1, multiplicatively damps or grows horizontal
(perpendicular to exhaust velocity) speed. zForce - default value 1
multiplicatively damps or grows vertical
(parallel to exhaust velocity) speed.
 (commit: 51df82f)