Add voyager api?

[metasoarous]

Looks like there's a client api for http://vega.github.io/voyager/:

https://github.com/vega/voyager/

We could add a voyager component, and corresponding to oz/voyage! REPL command which would bring up the Voyager explorer tool for some collection of data.

Have to think about call style; Maybe want to require passing a map with a data key, so that it would more or less operate the same as the other components with loading from url vs values vs...

[metasoarous]

Unfortunately, the voyager project has not been staying up to date, and is on a pretty old version of React which is incompatible with latest Reagent. Le sigh... Maybe could package this up an iframe or something?