Enhance search impl to account for additional or missing params

Presently search demands a query string, and ignores pagination params; looks like there is some expectation that missing query string should return all images(depends on repository config though?). In any case, we should probably respect the 'page' and 'n' params? https://docs.docker.com/v1.6/reference/api/registry_api/#search

We're also missing 'page' and 'num_pages' in the result object.