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.
I think we talked about this before when discussing the catalog, but if so, I don't remember why these kind of actions would use 'POST' instead of 'GET'. Can you elaborate?