More large scene optimizations
Follow-up to https://github.com/Slicer/Slicer/pull/489 For same large scene (1200 models):
- Reduces scene-loading time to ~4 minutes.
- Reduces delay when switching to Models module from 3 min to ~5s.
- Reduces delay when enabling "Include Fibers" option from 3 min to <5s.
- Reduces delay when changing visibility of all models from "very slow" to "usable" (few seconds)
All the tests pass (locally) except for:
The SSL one is known on buildbots, and I believe the other two are ITK linking issues specific to this build toolchain (mailing list).