Node to Row objects
- removed peerDeparture in solr remote search in case that peer does not
answer (this may be normal because it is allowed to switch this off)
metadata representation from the solr index. This shall replace metadata
from the built-in database in the future.
- added the Solr-driven metadata into the search index of YaCy which
makes it now possible to run YaCy without the old metadata index. This
is a major stept forward to a full migration to Solr.
- a new database for url reference data ('seen links')
- a new database extending the references to the full url metadata
attributes set which shall replace the old metadata database if it is
finished
- migration help classes stub to use old and new metadata databases
simultanously