Fixed /works/works/OLxxxW links in "Books to Read" carousel on the home page.
Added support for indexing editions in solr.

Also added new multi-valued field `seed` to the schema to store all
seeds that will have given work/edition in its's list of works/editions.
Useful for rendering lists using solr.
Fixed /works/works/OLxxxW link on subjects page.
Redirect to covers.openlibrary.org when the requested cover is not available in the coverstore of dev-instance.

This show nice covers for pages copied from openlibrary using
copydocs.py script.

Also added steps to initialize coverstore database on bootstrap.
Fixed solr query to fetch list of editions from solr, in case of single core solr.

Prior to this, it was not showing any editions on the work pages.