Don't use `ReferenceProperty` for parent because it overly complicates things and provides no real benefit.
Improve parent handling.
Merge branch 'dynamicObject-parent' into dataSourceBrowser
Updates after merge.
Support trees of arbitrary depth.
Fix some issues in parent handling.
Manually merge some changes from DataSourceBrowser branch.
Merge branch 'dynamicObject-name' into dynamicObject-parent

Conflicts:
	CHANGES.md
	Source/DynamicScene/CzmlDataSource.js
	Source/DynamicScene/DynamicObject.js
Merge branch 'dynamicObject-parent' into kml
Merge branch 'dynamicObject-parent' into dataSourceBrowser
Merge branch 'kml' into uberbranch

Conflicts:
	Source/DynamicScene/KmlDataSource.js
Merge branch 'dataSourceBrowser' into uberbranch