Fix modelMatrix in Primitive constructor
Add modelMatrix doc.
Update CHANGES.md
Merge master to primitive-modelmatrix
Remove use of non-existent MaterialAppearance.VERTEX_FORMAT

There were a few places in the code we were using `MaterialAppearance.VERTEX_FORMAT`,
which is `undefined`.  I've replaced this with `MaterialAppearance.MaterialSupport.TEXTURED.vertexFormat`,
which is the actual value used in cases where no `vertexFormat` is provided.  There
is no actual change in behavior.
Fix polyline caching in PathVisualizer.

This was a typo/regression from #2223. Also added a test.

Fixes #2250
Merge pull request #2251 from AnalyticalGraphicsInc/issue2250

Fix polyline caching in PathVisualizer.
Merge pull request #2249 from AnalyticalGraphicsInc/vertexFormat-cleanup

Remove use of non-existent MaterialAppearance.VERTEX_FORMAT
Merge pull request #2244 from AnalyticalGraphicsInc/primitive-modelmatrix

Fix modelMatrix in Primitive constructor