First cut at improved label outline support.
Add TileCoordinatesImageryProvider.
Use Cesium color instead of CSS color, and doc improvements.
More label improvements.
Add specs for TileCoordinatesImageryProvider.
Update CHANGES.md.
Fixes #473
Fixes #473
Cleanup outline code

1. Partially revert Sandcastle example
2. Update CHANGES
3. Fix a failing test (by removing an uneeded check).
4. Update simple.czml to take advantage of improved outlines.
Hopefuly finally changes before pull request
Fixes #473
Fix offscreen rendering artifact.
Merge pull request #562 from AnalyticalGraphicsInc/TileCoordinatesImageryProvider

Tile coordinates imagery provider
Merge remote-tracking branch 'origin/master' into labelOutlineWidth

Conflicts:
	CHANGES.md
Specs for outlineWidth

Also fleshed out other missing LabelCollection specs to bring coverage up to 100%.  Fixed a bug in `LabelCollection.remove`
Remove `clampToPixel` after review disussion.
Merge pull request #565 from AnalyticalGraphicsInc/labelOutlineWidth

Label clarity improvements
Fixes #473
Merge pull request #564 from RyanPepley/issue473

Fixes #473
Merge branch 'master' into polylineMaterials