adding a "location" field to the library.

adding a "location" field to the library.
This field is useful when the callnumber contains no information on the room where the item is stored.
With this field, we now have 3 levels of informations to find a book :
* the branch.
* the location.
* the callnumber.

This should be versatile enough to solve any storing method.
This hack is quite simple, due to the nice Biblio.pm API. The MARC => koha db link is automatically managed. Just add the link in the parameters section.