Update UI in Billboards, Labels and Camera Sandcastle examples

For #1685 

Updated UI in Billboards, Labels, Camera (converted buttons to combobox)
Re-positioned buttons in Materials
Updated a few outdated pictures
Added GeoJSON/TopoJSON example
Both of these could be under a new `Sandcastle\Data` directory.  This will require minor tweaks to the [Models tutorial](http://cesiumjs.org/2014/03/03/Cesium-3D-Models-Tutorial/).