Label clarity improvements

1. Fix issues with how we measured test so that the result is more accurate.  We were using the fill-only measurement for both fill and stroke.  This dramatically improves our ability to outline smaller fonts, see the update simple.czml for an example.
2. Add the ability to specify `outlineWidth` for Labels and CZML labels.
3. Default `LabelCollection.clampToPixel` to false, I'm not sure we even need it anymore as the fixes for 1 eliminate the reason it was added.
4. Tweaked the Sandcastle Labels example to have a custom outlineWidth
5. Updated changes.