Replace `undefined` equality checks with `defined` function.

There are some errors in the conversion that still need to be addressed.
Fix remaining errors, all specs now pass.
Fix a few more find/replace errors.
Make Viewer handle data source clock management.

Previously, viewerDragDropMixin, CesiumViewer, and Sandcastle examples all had code to set the display's clock to match the first loaded data source.  Now, Viewer does that automatically by listening to the DataSourceCollection's event.

Viewer now owns its DataSourceCollection, instead of DataSourceDisplay owning it.

Also rename "Simple CZML Demo" Sandcastle example to "CZML" since there is no other CZML example anymore.
type is unnecessary.
Fix regex for detecting Cesium.js to avoid a false positive.

Add some specs to check that the regex matches expected URLs.
Changes after review.
Merge pull request #1030 from AnalyticalGraphicsInc/fixCesiumBaseUrl

Fix regex for detecting Cesium.js to avoid a false positive.
Merge branch 'master' into issue893

Conflicts:
	Source/Core/buildModuleUrl.js
Merge pull request #1029 from AnalyticalGraphicsInc/dataSourceClockManagement

Make Viewer handle data source clock management.
Merge branch 'master' into issue893

Conflicts:
	Apps/CesiumViewer/CesiumViewer.js
	Source/DynamicScene/DataSourceDisplay.js
	Source/Widgets/Viewer/viewerDragDropMixin.js
Fix bad checks due to browser differences.
Fix a few more bad checks.
Switch the last few places to use defined.
Clean up specs, fix one last bad check.
Merge pull request #1026 from AnalyticalGraphicsInc/issue893

Fix #893
Merge branch 'master' into dynamicScene-cleanup

Conflicts:
	Source/DynamicScene/ConstantProperty.js
	Source/DynamicScene/CzmlUnitSpherical.js
	Source/DynamicScene/DynamicBillboard.js
	Source/DynamicScene/DynamicBillboardVisualizer.js
	Source/DynamicScene/DynamicColorMaterial.js
	Source/DynamicScene/DynamicCone.js
	Source/DynamicScene/DynamicDirectionsProperty.js
	Source/DynamicScene/DynamicEllipse.js
	Source/DynamicScene/DynamicEllipsoid.js
	Source/DynamicScene/DynamicGridMaterial.js
	Source/DynamicScene/DynamicImageMaterial.js
	Source/DynamicScene/DynamicLabel.js
	Source/DynamicScene/DynamicLabelVisualizer.js
	Source/DynamicScene/DynamicObject.js
	Source/DynamicScene/DynamicObjectView.js
	Source/DynamicScene/DynamicPath.js
	Source/DynamicScene/DynamicPoint.js
	Source/DynamicScene/DynamicPointVisualizer.js
	Source/DynamicScene/DynamicPolygon.js
	Source/DynamicScene/DynamicPolyline.js
	Source/DynamicScene/DynamicPolylineVisualizer.js
	Source/DynamicScene/DynamicPositionProperty.js
	Source/DynamicScene/DynamicPyramid.js
	Source/DynamicScene/DynamicPyramidVisualizer.js
	Source/DynamicScene/DynamicVector.js
	Source/DynamicScene/DynamicVertexPositionsProperty.js
	Source/DynamicScene/ReferenceProperty.js
	Specs/MockProperty.js