moved README file
Update README.md

Adds some description of how to use schema and RAML in our SOA
Update README.md

Updated formatting
Reorganized repo and renamed schema files according to conventions spelled out in the readme.
Replaced voxels-metadata-schema with the more complete version copied from janelia-flyem/dvid-api
schemas: dvid-voxels-metadata: Allow empty string for resolution.
schemas: Added a "version" field to all schemas and a corresponding verison field in the schema properties itself.