Build a Volume/VDB Visualizer

[johnnyquest]

Some bullet points

• let's focus on VDB-style volumes mostly (provide option to convert input(s) to vdb)
• volume (field) selector (visualizing just a single volume/field)
• support for scalar (density/temp/etc) and vector (vel) type fields
• optional VDB diagnostics before, e.g. catch NaN voxels (e.g. coming from potential flow node?)
• point jitter (0..1 where "1" is one voxel jitter)
• volume intrinsic transformations!
• downres before visualize
• color visualizer: ramp w/ min/max values, automatic/get buttons
  • should work both for scalars and vectors (vector length)
  • Alpha support for visualization
  • pscale support for visualization (disc point display type)
• direction visualizers: simple vel direction vector OR volume trail -> just volume trail, that should be fine
  • alpha support / curve width support: needs to be turned on on obj level? :(
• clipping/trimming
  • usual single-voxel clipping plane thing
  • optional second input with a bbox, for clipping (clip the volume before converting to points?)
  • trimming below min / above max values (both optional)