Polyline Materials

I don't expect this pull request to be merged for a while, but I wanted to get feedback from @pjcozzi and anyone else who is interested. This branch contains wide polylines and a few new materials like outlines and arrows. Volumetric lines and a few other materials that are specific to polylines are still experimental and in different branches that are not a part of this pull request.

Any CZML polylines/paths will have the default red color material. @mramato is looking into what needs to be done there.