Handle CZML availability with multiple intervals.

`DynamicObject.availability` is now a `TimeIntervalCollection` instead of a `TimeInterval`.  The availability property is still always replaced when a new availability is provided, no merging happens.
Merge remote-tracking branch 'origin/master' into dynamicObject-availability

Conflicts:
	CHANGES.md
Update CHANGES.md

`DynamicObject.availability` update is a breaking change.
Remove unecessary if checks.
Fix whitespace.
Remove duplicate function call.
Fix path visualization.
Merge pull request #1334 from AnalyticalGraphicsInc/dynamicObject-availability

Handle CZML availability with multiple intervals.