Blaze server

Here is a tiny replacement for catalog.  It doesn't do any of the directory management tasks but it does cleanly expose `getitem` over a simple HTTP API.  This API takes structured JSON data and so should be easy to interact with.  Because this interacts with the `blaze.data` getitem syntax this should extend to a variety of data formats.

cc @mwiebe

Disclaimer, my web-programming skillz could use some work.  Suggestions welcome.
We need to send a packet of data along with the request.  In this case that packet describes index information of what we're trying to get back.  Using `GET` we would be restricted to passing information through the URL.  This is nice if the data fits nicely into a url, sadly our nested index structure is a bit too complex for this.  Passing it as JSON is significantly more convenient.