Changes.md : Consolidate notes for 0.60.0.0
Changes.md : Consolidate notes for 0.60.0.0

When folks adopt `0.60.0.0` from `0.59.x.x`, we don't want them to have to read the release notes for beta releases.

ImageEngine/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,hradec/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,hradec/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,hradec/gaffer