add index to level source images
Merge pull request #375 from code-dot-org/add_index_to_level_source_images

add index to level source images
[Progress on 67046576]: enable sharing for bounce
merge
Automatically upgraded blockly-dist.
Merge pull request #381 from code-dot-org/pivotal_67046576

Pivotal 67046576: enable sharing of bounce - on new last level
Merge branch 'delivered' into finished