fix issue with trigger causing duplicates
Refactor PreDB final stage - remove md5/sha1 from predb table.
NB this is a long patch - go make a coffee, spend time with the family or go outside - no seriously
update schema to match last patch.
Disable update_predb_hashes and update_predb_md5 scripts as they are now defunct.
Merge pull request #637 from nZEDb/dev

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