Server needs a "metadata" endpoint

[mycrobe]

It would be nice to be able to get some information about the gramene server… from the server.

I propose a zero-param metadata or about endpoint that returns a simple doc that could look like this:

{
  "gramene" : {
    "dbVersion": 50,
    "ensemblVersion": 84,
    "releaseDate": "Thu Mar 22 2016 12:23:01 GMT-0500 (EST)"
  },
  "software" : {
    "gramene-swagger": "0.50.5"
  }
}

Working out what is needed in this document is part of this issue.