Clean up dynamic geometry updaters

The dynamic geometry updaters in the DataSource layer did not have
the same semantics as the rest of the visualizations system.  Mainly,
an undefined value would cause Cesium to crash instead of simply not
rendering an object.  This change uses the newer Property.get helper
functions in order to both clean up the code and follow the same rules.

Fixes #2252
Use removeAndDestroy in ModelVisualizer.
Make removeAndDestroy return value consistent with remove
Merge pull request #2330 from AnalyticalGraphicsInc/geometry-updater-cleanup

Clean up dynamic geometry updaters
Test against epsilon value instead of comparing to zero in CesiumMath.zeroToTwoPi.
Also make new test use epsilon test.
Merge pull request #2332 from AnalyticalGraphicsInc/zeroToTwoPi

CesiumMath.zeroToTwoPi
Merge branch 'master' into geometry-perf