Cesium Features

Hi,

I started a Cesium Features page that is linked to from the main wiki page.

This is a concise, bullet-point style overview of the major Cesium features similar to what many of us have done before with STK Components. Some of the features listed, namely WMS and materials, still need to come into master.

The page could use some more work, including more images and more details in places, so feel free to jump in.

Regards,

Patrick