Make a public list of migrated accounts in Babylon

Spendable and delegatable KT1 contracts were migrated in 005. The manager accounts that were not allocated (had no balance) were credited with 1 mutez. Because there were no receipts for these balance updates, they weren't visible to explorers. It would be useful to make a public list of these balance updates.

This can be a json mirroring the format of balance update receipts, e.g.:

[{
  "kind": "contract",
  "contract": "tz1...",
  "change": "1"},
}, 
...]