Bug 19893: Alternative optimized indexing for Elasticsearch

Bug 19893: Alternative optimized indexing for Elasticsearch

Implement optimized indexing for Elasticsearch

How to test:
1) Time a full elasticsearch re-index without this patch by running the
   rebuild_elastic_search.pl with the -d flag:
   `koha-shell <instance_name> -c "time rebuild_elastic_search.pl -d"`.
2) Apply this patch.
3) Time a full re-index again, it should be about twice at fast (for a
   couple of thousand biblios, with fewer biblios results may be more
   unpredictable).

Sponsored-by: Gothenburg University Library
Signed-off-by: Ere Maijala <ere.maijala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>