Implement objects - PointsPrimitive, CurvesPrimitive

[boberfly]

Currently there is conversion code to convert IECore::CurvesPrimitive to Cycles, but this is not tested yet and it isn't too clear if they need to be attached to a ccl::ParticleSystem (via IECore::PointsPrimitive) which also hasn't been implemented yet.

[boberfly]

PointsPrimitive are now implemented:
https://github.com/boberfly/GafferCycles/blob/master/include/GafferCycles/IECoreCyclesPreview/ParticleAlgo.h
However Cycles doesn't have a way to render these, but under the hood this is used to apply per-particle info onto instanced geometry from Gaffer's Instancer if you make sure to transfer particular named primvars to attributes (this will be available from the particle_info shader):
"index" or Gaffer's "instanceIndex"
"age"
"lifetime"
"location" or Gaffer's "P"
"rotation" or Gaffer's "orientation"
"size" or Gaffer's "width"

I will re-visit this if this patch ever goes mainline and I can render them as spheres:
https://developer.blender.org/D3818

[boberfly]

@murraystevenson kindly tested a scene with curves and supplied a PR fix here:
#23

So CurvesPrimitive should convert now, but it has been reported that the curve settings in CyclesOptions aren't being set right yet.

[boberfly]

CyclesOptions are working, true PointsPrimitive with https://developer.blender.org/D3818 I am moving to post-1.0.