Allow CZML polylines and paths to use materials.

We already allowed this via DataSources, but CZML itself had not yet been udpated.
Update CZML materials

This goes along with CZML changes listed in AnalyticalGraphicsInc/czml-writer/pull/73.
Merge pull request #1909 from AnalyticalGraphicsInc/czml-material-cleanup

Update CZML materials
Merge pull request #1904 from AnalyticalGraphicsInc/czml-materials

Allow CZML polylines and paths to use materials.
Merge branch 'master' into polylineArc

Conflicts:
	Apps/CesiumViewer/Gallery/simple.czml
	Source/DataSources/CzmlDataSource.js