Expose width/height properties on DynamicBillboard.
Add NearFarScalar support to DynamicBillboard

1. Implement Packable in NearFarScalar so that it can be a sampled property.
2. Add nearFarScalar property to DynamicBillboard
3. Hook up the visualizer.
4. Specs for everything.
Merge remote-tracking branch 'origin/dynamicScene-es5-properties' into dynamicBillboard-size
Merge branch 'dynamicScene-es5-properties' into dynamicBillboard-size
Merge branch 'dynamicScene-es5-properties' into dynamicBillboard-size

Conflicts:
	Source/DynamicScene/DynamicBillboard.js
Fixes after merge.
Merge branch 'dynamicScene-es5-properties' into dynamicBillboard-size
Merge branch 'dynamicScene-es5-properties' into dynamicBillboard-size
Merge branch 'master' into dynamicBillboard-size
Merge pull request #1164 from AnalyticalGraphicsInc/dynamicBillboard-size

Add explicit size and NearFarScalar support to DynamicBillboard