NoZebra SQL index management :

NoZebra SQL index management :
* adding 3 subs in Biblio.pm
- GetNoZebraIndexes, that get the index structure in a new systempreference (added with this commit)
- _DelBiblioNoZebra, that retrieve all index entries for a biblio and remove in a variable the biblio reference
- _AddBiblioNoZebra, that add index entries for a biblio.
Note that the 2 _Add and _Del subs work only in a hash variable, to speed up things in case of a modif (ie : delete+add). The effective SQL update is done in the ModZebra sub (that existed before, and dealed with zebra index).
I think the code has to be more deeply tested, but it works at least partially.