unify(particlesys): Merge and move W3DParticleSys to core

[stephanmeesters]

Merge by rebase

This merges and moves W3DParticleSys.h and W3DParticleSys.cpp.

Generals gets:

• Ability to render smudges (TheSmudgeManager is non-null but we don't expect to see any smudges in the data)
• Ability to render weather effects (not used, TheSnowManager is null)
• Removes unnecessary check for invisible particles (added to GeneralsMD to test but it never triggered a breakpoint)

[xezon]

Commit titles need polishing

[Skyaero42]

Agreed