Experimental preview: Vertex sharing for fixed topology files

fixed lag when playing alembic from timeline.

Experimental preview: Vertex sharing for fixed topology files V3

• Fixed issue with Shared Vertices vs UV Tile sub-meshes
• Also, default now does NOT generate sub-mesh per UV tile.

Experimental preview: Vertex sharing for fixed topology files V2

same as previous preview release, with added options to not apply UV/Normals/Tangents from file at each sample read: "Vertex extra data is static"

Experimental preview: Vertex sharing for fixed topology files

added import options, off by default: "Merge Vertices (experimental)"

when set to true, will share vertices between polygons when possible.
Note that, this an investigation into a potential optimization.
Seeing reductions, in some cases of 3-4x the number of vertices sent to the GPU.
But, merge process is single threaded and injects per un-merged vertex 2 hash table lookup's (overhead).

Only works in MS. Windows!

Experimental preview: Vertex sharing for fixed topology files

added auto-activation option when alembic is played through a timeline clip

Experimental preview: Vertex sharing for fixed topology files V4

fixed crash with alembic files containing no normals data

Fixed to work with Unity 2017.1.0b3 release

Will NOT work with prior releases of Unity, only 2017.1.0b3 and later.

Enable scripted importer for 2017.1 beta 2

Requires Unity 2017.1.0b2

20170426

• fix: AlembicPointsRenderer didn't handle transform (https://github.com/unity3d-jp/AlembicImporter/issues/17)

20170419

• Refactor folowing Unity 2017.1 beta release
  Timeline enabled with builds of unity 2017.1.0b1 or later.
  Scripted importer enabled with builds of unity 2017.1.0b2 or later.