Standardize CSS names

So far, our widgets have been playing fast and loose with the CSS namespace.  This standardizes everything to avoid potential collisions.  The new rule is everything should follow the `cesium-<item>-<cssClassName>` convention.

Examples:
cesium-lighter
cesium-widget-[xxx]
cesium-timeline-[xxx]
cesium-animation-[xxx]
cesium-fullscreen-[xxx]

I'll also update the coding conventions once this is in.