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.
Looking online it seems like one large difference between PUT and POST is idempotence.  Given our application using PUT seems appropriate.

Any other suggestions @seibert ?