send sealing status in deal status response

[dirkmc]

Supersedes #697
Fixes #696

$ boost --json deal-status --deal-uuid=f1ffaa64-3249-4173-b008-572b35e1e81e --provider=t01000
{
  "chainDealId": 1,
  "clientWallet": "t3r3hr3xl27unpefvipve2f4hlfvdnq3forgr253z6dqahufvanatdandxm74zikheccvx74ys7by5vzafq2va",
  "dealUuid": "f1ffaa64-3249-4173-b008-572b35e1e81e",
  "label": "bafk2bzacedsnewk7clxwab2wgwyoi7u5tzdhldx7fkxpqdq7unrxz2zoy4d2g",
  "provider": "t01000",
  "publishCid": "bafy2bzacea7cohv4zexvyyv5hwgdauaajcb6w74bn2yxfymy57ywam6xpyneq",
  "sealingStatus": "Proving",
  "status": "IndexedAndAnnounced",
  "statusMessage": "Sealing: Proving"
}