Updates to info in .blend files

[marklescroart]

Needs to happen:

names for bvp fields for objects, backgrounds, actions reconciled with new class attributes.

backgrounds:
semantic_category (get rid of this?)
wordnet_label (not ..._labels)
sky_semantic_category (high priority) - should this be WordNet labels??
object_semantic_category (low priority)

skies:
semantic_category (get rid of this?)
wordnet_label (not ..._labels)

objects
semantic_category (get rid of this?)
wordnet_label (not ..._labels)

shadows
(add anything here? Are there any attributes of shadows?)

actions
wordnet_labels->label

more...?