Groups/orgs in SOLR

Add groups & orgs to the SOLR index.

We have all sorts of trouble returning lists of groups/organizations, because a group in its full glory is slow to produce: with extras, parent hierarchy, is slow to do. They you want to sort on all these things, and it's another complication. The code would be so much simpler if the groups/orgs were indexed in SOLR for listing, with the full group_dict 'cached' in there too. See the woes of using postgres/dictization here: https://github.com/ckan/ckan/issues/2554#issuecomment-132171669

Also, this would improve the group search, providing stemming etc.

Related to #97.

Start with related issue #97 and the PostgreSQL/dictization discussion linked from #2554. Identify the existing group and organization listing and search entry points, then determine how SOLR indexing currently works. Done means groups and organizations can be indexed with their full group_dict data and support listing, sorting, and improved search.

Written by the indexing model from the issue text.