bibindex: adds tokenizers for parent records

* Adds BibIndexExactAuthorParentTokenizer, internally it calls
  BibIndexExactAuthorTokenizer.

* Adds BibIndexAuthorParentTokenizer, internally it calls
  BibIndexAuthorTokenizer

* Hardcodes in bibindex_engine that the tokenizers of the fields 'exactauthor'
  and 'author' want a record id insthead of a tag value.

* Sets BibIndexExactAuthorParentTokenizer as tokenizer for the
  'exactauthor' index (tabfill.sql and upgrade script)

* Sets BibIndexAuthorParentTokenizer as tokenizer for the
  'author' index (tabfill.sql and upgrade script)

* Adds tests