Improve stencil schema commands

[ravisuhag]

List schemas in a given namespace.

$ stencil schema list -n namespace

View schema metadata for a given schema.

$ stencil schema info <name> -n namespace

List versions of a given schema.

$ stencil schema version <name> -n namespace

View a schema document/file for a given schema id.

$ stencil schema view <name> -n namespace -v version 

Download a given schema to a specified path.

$ stencil schema download <name> -n namespace -v version -o ./file

Delete a given schema.

$ stencil schema delete <name> -n namespace

Edit metadata of a given schema.

$ stencil schema edit <name> -n namespace -f format  -c compatibility

Show diff between two schemas that are already available on the server.

$ stencil schema diff <name> -n namespace --source earlier-version --target <later version> --prefix 

Check the compatibility of a schema.

$ stencil schema check <path> --against <name> -v version -n namespace

Generate the graph of relationships in a given schema.

$ stencil schema graph <name> -n namespace  -v version

Upload a particular schema version

$ stencil schema upload <name> -n namespace -f path_to_file

[ravisuhag]

@harikrishnakanchi What are your thoughts on this?