feat(daemon) `ipfs daemon --initialized`

With this PR, users can fetch and run ipfs in _one_ command.

```
docker run -d -p 4001:4001 -p 5001:5001 jbenet/go-ipfs daemon --initialized
```

Magic.

nb: needs https://github.com/jbenet/go-datastore/pull/9
@maybebtc why is this `Errorf` coming not from `fmt`? i agree that formatting an error maybe should've been in `golang/errors` instead of `golang/fmt`, but is there a strong reason for swimming against the tide?