Fix koansys#106 using new Cesium Bing Maps key, other Assets/

Cesium's Bing Maps key expired so their new code gives us a fresh
one.

Might as well use all their Assets as well, so we don't have to
maintain our own SkyBox and static Earth map.  Update the docs to copy
their CesiumUnminified/ directory into our tree as cesium/, then
remove our unnecessary copies.

Author: Chris Shenton

doc/building-cesium.rst

@@ -15,12 +15,14 @@ Build it using the Java `ant` tool (you'll need Java installed)::
 This builds everything: the Cesium library and all the demos and
 documentation.
 
-Copy the three files from .../cesium/Build/Unminified/ to your SOT
-project's .../sot/viz/cesium/ directory:
+Copy recursively the contents .../cesium/Build/CesiumUnminified/ directory::
 
- * 2761612 Dec  5 13:13 Cesium.js
- *   87087 Dec  5 13:13 cesiumWorkerBootstrapper.js
- *  128440 Dec  5 13:13 createVerticesFromExtent.js
+  drwxr-xr-x       102 Jan 25 11:50 Assets
+  -rw-r--r--   2874967 Jan 25 11:54 Cesium.js
+  drwxr-xr-x       136 Jan 25 11:50 Widgets
+  drwxr-xr-x       136 Jan 25 11:50 Workers to your SOT
+
+to your project's .../sot/viz/cesium/ directory.
 
 These are referenced by our index.js file. We use the unminified
 versions so we can debug.