Unify the conversation id for inbox and private v1

Current conversation ids:
```
"354c877b, /convo/inbox/v1/ae5f0831"
```

Topics:
```
"/inbox/3c76f723", "/convo/private/354c877b"
```

Tasks:
- decide if use prefix like convo/inbox and convo/private
- decide if use same one for conversation id and topic
- decide if use version number or not.