Rename `HelloWorld.html` to `index.html`

Also add Chrome Frame tag to Hello World so it works in IE if GCF is installed.

This change was largely a result of some end-user usability feedback in a recent Cesium hackathon.
Add index.html for the small release zip.
Update Cesium.js index.html with external links.
Fix tab/space inconsistency.
Merge branch 'master' into helloWorld
Have the Cesium.js index.html detect if it is being ran from inside a web-browser and put up a message and link if it is not.
Fixed typo
Merge branch 'master' into helloWorld
Merge pull request #629 from AnalyticalGraphicsInc/helloWorld

Rename `HelloWorld.html` to `index.html`