BibFormat: new Solr fulltext snippet facility

* New optional Solr fulltext snippet facility.  (closes #1301)

Signed-off-by: Patrick Glauner <patrick.oliver.glauner@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'master' into next

* master:
  BibFormat: new Solr fulltext snippet facility