Improve DynamicScene path visualization

Previously, we were only using data points explicitly specified in the CZML to draw paths.  This change makes the sampling algorithm take a maximum step size of 60 seconds so that if points are further apart, we step in-between them.  This allows us to generate certain types of data (such as satellites) with a greter step size in the CZML.  For example, I regenerated simple.czml and it is now 50% smaller with no visual differences.

While the path code is still not in its final form, this change provides a big benefit from a minor tweak.  The easiest way to test this is to use the new simple.czml in master and notice how jagged the orbits are, loading in this branch shows smooth orbits.
Add plane type and update functions that accepted plane normal and constant to use the plane type.
Update CHANGES.md.
Merge pull request #504 from AnalyticalGraphicsInc/plane

Plane
Eliminated allocations when setting matrix uniforms
Changes based on review
Merge pull request #506 from AnalyticalGraphicsInc/uniforms

Eliminated allocations when setting matrix uniforms
Update Plane distance parameter doc.
Merge pull request #503 from AnalyticalGraphicsInc/sampledPaths

Improve DynamicScene path visualization
Adjust default camera position and make consistent.

Previously the widgets adjusted the default camera position after constructing the scene, meaning that users had inconsistent defaults depending on whether they used a widget or not.
Merge pull request #508 from AnalyticalGraphicsInc/camera-default-position

Adjust default camera position and make consistent.
Merge branch 'master' into cesium-widget