- Indexing status is written to table "elasticsearch_helper_index_status".
- Multiple reindex modes are added to reindex confirmation form: with
  options to do a simple reindex, simple reindex for failed items only and
  complete reindex (subsequent drop, setup, reindex operations).
- Clear queue button is added separately from other index-specific buttons.
- Entries for specific index plugins in indexing status table are cleared when
  index drop operation is invoked on index plugin.
- Entries for specific entities are removed from indexing status table when
  said entities are removed.

Co-authored-by: Marc Galang <marc.galang@wunder.io>
Co-authored-by: Raimonds Kalnins <raimonds.kalnins@gmail.com>