Add material support for DynamicPath

Replaced `color`, `outlineColor`, and `outlineWidth` in `DynamicPath` with a `material` property.
This allows data sources to use materials other than PolylineOutline for paths.  CZML is not impacted by this change and doesn't have this ability yet, that will be addressed in a future pull.
Changes after review.
Merge remote-tracking branch 'origin/master' into dynamicPath-material
Added a test for custom materials.
Merge pull request #1794 from AnalyticalGraphicsInc/dynamicPath-material

Add material support for DynamicPath