Fix LabelVisualizer crash

#2223 introduced a regression (due to a typo) that was not covered by any unit tests. (which @shunter promptly ran into).  This change adds unit tests and fixed the bug.
Merge pull request #2235 from AnalyticalGraphicsInc/label-visualizer-crash

Fix LabelVisualizer crash
Pass CesiumWidget.clock option in through Viewer constructor.

Also fixed a related bug when multiple animation widgets are in use.
Merge pull request #2236 from AnalyticalGraphicsInc/viewer-clock

Pass CesiumWidget.clock option in through Viewer constructor.
Fix warnings
Have PrimitiveType default to Triangles
Update CONTRIBUTORS.md
Update GeometrySpec.js
Merge pull request #2240 from flinsalata/master

Have geometry primitive type default to triangles
Merge pull request #2238 from AnalyticalGraphicsInc/warning-fix

Fix deprecation warnings in unit tests
Fix Geometry doc.
Merge branch 'master' into safari-nonsense