OSPRay v2.7.0

• Add support for transformation and camera Motion Blur (with the path
  tracer) via shutter parameter of the camera and motion.transform
  array and time parameter of the instance and camera
• OSPRay can now be built for ARM64 CPUs with NEON (e.g., Apple M1)
  using the superbuild. Thus, new minimum versions are for ISPC
  1.16.0, for Embree 3.13.1 and for rkcommon 1.7.0
• OSPRay now requires minimum Open VKL v1.0.0 to bring the
  following improvements:
  • Configurable background values for all volume types (default
    NaN), defining region outside the volume domain
  • Better default sampling rate for scaled VDB volumes, improved
    robustness
  • Structured regular volumes now support tricubic filtering and
    more accurate gradient computations as well as more robust
    isosurfaces
• The multidevice module contains a new OSPRay device implementation
  that delegates work to any number of subdevices. This is an
  experimental feature in this release but we invite feedback
• SciVis Renderer now ignores normal/albedo/depth hits on surfaces
  that are fully transmissive (material d = 0)
• Changed the behavior of background rendering in SciVis renderer to
  more closely reflect that of the path tracer: Background hits are
  rendered in background color in the albedo buffer and black in the
  normal buffer
• The SciVis renderer does not compute depth of field (DoF) anymore,
  as this effect does not align with the SciVis renderer definition
  and exposed artifacts
• Fixed crash on exit when using the MPI device
• Fixed rendering of depth buffer in the example application
• The first argument to material constructor ospNewMaterial, i.e.,
  renderer_type, is now deprecated and will be removed in a future
  release. AO and SciVis renderers still assume "obj" like behavior
  for all material types
• Deprecated the xfm parameter of the instance, use transform
  instead
• Dependencies Google Benchmark, GoggleTest, and Snappy moved
  out-of-source to superbuild ExternalProjects