Tweak CZML reference frame handling

Not specifying a reference frame usually defaults to FIXED, however if you specified the INERTIAL frame in a previous packet, we should not overwrite that with FIXED if it is left out of subsequent packets.
Fix spec errors when running against a combined file with debug code removed.
Merge pull request #1496 from AnalyticalGraphicsInc/fixReleaseSpecs

Fix spec errors when running against a combined file with debug code removed
Merge pull request #1495 from AnalyticalGraphicsInc/czml-referenceFrame

Tweak CZML reference frame handling
Merge remote-tracking branch 'origin/master' into gltf