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'm also pretty ignorant of web stuff and am mostly regurgitating things that people have told to me.  If you have experience here then please speak up and correct me.