[common][series] Use SeriesMeta as anonymous field
[common][series] Use SeriesMeta as anonymous field

- [ ] TODO: this breaks most existing tests
- [ ] TODO: it has problem for JSON marshal and unmarshal because it
will not put the fields of the anonymous struct in top level.
````
[
  {
    "SeriesMeta": {
         "name": "cpu.idle"
         ....
     },
    "points": [[1123123, 1], [12312, 2]]
  }
]
````

xephonhq/xephon-k,xephonhq/xephon-k,xephonhq/xephon-k,xephonhq/xephon-k,xephonhq/xephon-k,xephonhq/xephon-k