Request for API name change: "schema" should be "metadata"

[stuarteberg]

In the DVID REST API, the following call returns a json file describing the axes, resolution, pixel type, etc.

/api/node/<UUID>/<data name>/schema

The word "schema" here is misleading, because that word is traditionally used to describe the structure of e.g. a json or xml tree. This data is not a schema in that sense -- I think the better term is "metadata".

Also: at some point, we will start publishing the json schemas for the messages produced by certain DVID API calls. To avoid confusion, we should not overload the term "schema" for API calls that return anything other than a true json schema.