Add fields and refactor solr branch to make this into ukwa-collections-solr

[anjackson]

For ukwa/w3act#582, we need to add some fields to the Solr Collections instance, and to make things clearer this whole repo should be refactored to provide a Dockerized Solr server.

i.e. merge the solr branch into master and strip out most content so ukwa-collections-solr is the top-level thing. Then rename the repo to ukwa-collections-solr.

[anjackson]

This is another task relating to Dockerization that will help with ukwa/ukwa-ui/issues/11