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
@jbenet 

importing our errors package as `errors` is okay since the only thing exported by Go's package is `errors.New`. In the case of `fmt`, importing one of our packages as `fmt` would stir up trouble with all of the commonly-used functions like `Sprintf`, etc.

Using our own `Errorf` causes little to no harm, but provides all of the benefits of our custom debugging errors. It is a mere cosmetic wart, no?