Add initial filegrain-esque continuity manifest

[hinshun]

2019/06/14 15:44:21 Converted Manifest [446] sha256:2eba1618ed99dcc7fe56a142f8d51dcd1fda859e41c993d3986969c64bde62ec:
{
   "schemaVersion": 2,
   "config": {
      "mediaType": "application/vnd.docker.container.image.v1+json",
      "digest": "sha256:8516b36eef83784661a7d10020d94a8a4eab8a6eef9e37058f7f739c672220ea",
      "size": 1512
   },
   "layers": [
      {
         "mediaType": "application/vnd.continuity.manifest.v0+pb",
         "digest": "sha256:8778aa83f0ff4cb1d767de4a6ce6ca09a7885db240654c3deb10f49466ca6494",
         "size": 22322
      }
   ]
}