Add particle y-billboard option to standard shader

[Arnklit]

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This adds a particle y-billboard option to Standard Material.

When used with Align Y on the particles it allows you to have particles that align themselves with velocity, but face the camera.

Note I'm not sure if this should be added since you can also achieve this with the "Particles -> Drawing -> Transform Align -> Z Billboard + Y to Velocity". But these options don't work with stuff like Particle Animation.

In general I'm not sure why there are billboarding settings both in the Particles and in the Material like this.