Bug 20248: Improve Elasticsearch mappings UI and rebuild_elastic_search.pl.

Bug 20248: Improve Elasticsearch mappings UI and rebuild_elastic_search.pl.

Improvements:
1) Mappings UI now has button that allows one to reset the mappings.
2) Mappings UI displays the items in alphabetical order.
3) Indexing script drops and recreates the index right away, which
helps prevent ES from autocreating a bad index if someone does something
while the first batch of records is being processed.
4) Indexing script has nicer output.

To test:
1) Change mappings.yaml file
2) Reset mappings in UI in mappings.pl
3) Verify the mappings have been changed in UI
4) The field order is alphabetical
5) Rebuild script has clean output
6) Run test t/db_dependent/Koha_Elasticsearch_Indexer.t

Signed-off-by: Bouzid Fergani <bouzid.fergani@inlibro.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>