Rename all instances of cesium.agi.com to cesiumjs.org.

Cherry-picked from @kring's d0e34a7a.
Tracking shouldn't be in master.

Also, found a straggler.
Update CHANGES.md
Update CHANGES.md again
Merge pull request #1320 from AnalyticalGraphicsInc/update-address

Update master's references to the website.
Drop MOZ_ WebGL extension prefixes to avoid warnings in Firefox
Changed extensions to use undefined when not available
Added failIfMajorPerformanceCaveat
Workaround tests until failIfMajorPerformanceCaveat is returned by getContextAttributes
Undefined tweak
Added allowTextureFilterAnisotropic
Update CHANGES.md
Added maximumScreenSpaceError
Adding dynamic vector display support.
Merge pull request #1325 from fstoner/dynamicVector

Adding dynamic vector display support.
Remove duplicated change.
Changes based on review
Merge pull request #1321 from AnalyticalGraphicsInc/christmas

Merry Christmas
Clean up mouse event storage.
Fix crash when additional properties are added to AutomaticUniforms.