[#1078] package_show performance part two

A separate pull request for just the second part of work in #1079 plus fixes (4.9x improvement for our site, 3.8x improvement without any plugins)

This PR adds a "validated_data_dict" field to SOLR, as suggested by @kindly, which stores the dataset after validation.  This lets us skip all of the package_show validators in the common case.  The data_dict value is still used when a schema is passed to package_show.