Add support for multiple render targets.
Fix everything that uses a framebuffer with a color attachment.
Add Context tests.
Fix Framebuffer tests.
Add tests for multiple render targets.
Updates from review.
Make Framebuffer immutable.
Fix typo.
Update code and tests to make framebuffers immutable.
Merge branch 'master' into mrt
More updates from review.
Add test for clearing framebuffer with multiple color attachments.
Merge pull request #1375 from AnalyticalGraphicsInc/mrt

Multiple Render Targets
CZML loading should suspend events

Loading CZML was previously sending events the moment a DynamicObject was created (even though the object had no actual data in it).  It would also send out one event per object, which affects performance.  This change uses the `DynamicObjectCollection.suspectEvents` functionality to send one update with all data loaded at the end.  I thought this was the behavior already, but it wasn't.

I also fixed #1380 while I was in the code.  This was do to all visualizers not cleaning up properly in their destroy.  It was a one line change for each visualizer.
Update CHANGES.
Simplify test by using spy.
Fix typo.
Merge pull request #1381 from AnalyticalGraphicsInc/czml-suspendEvents

CZML loading should suspend events
Switch srcfiles to srcresources since cesiumJsFiles is not a fileset anymore.
Merge pull request #1384 from AnalyticalGraphicsInc/fix1383

Switch srcfiles to srcresources since cesiumJsFiles is not a fileset any more