Add TileCoordinatesImageryProvider.
Use Cesium color instead of CSS color, and doc improvements.
Add specs for TileCoordinatesImageryProvider.
Update CHANGES.md.
Merge pull request #562 from AnalyticalGraphicsInc/TileCoordinatesImageryProvider

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

Conflicts:
	CHANGES.md