Bug 6536: Dbrev for Z3950 search improvements

Bug 6536: Dbrev for Z3950 search improvements

Adjusts table z3950servers:
Drops unused columns icon, description and position.
Moves id column to first position.
Renames name to servername, and type to servertype. (This is not only more
clear but may eliminate some problems too with DBIx.)
Changes recordtype from varchar(45) to enumeration with two members. [The
upgrade replaces unknown record types with biblio, although it is very
unlikely to find such records.]
Adds SRU as servertype enumeration member. Removes opensearch, since it is
not used/supported. [The upgrade replaces unknown server types with zed
(z3950) (in exceptional cases).]
Adds new columns: sru_options, sru_fields, add_xslt.

Test plan:
Run database update via webinstaller.
Check your z3950servers table.

Signed-off-by: Giuseppe Angilella <giuseppe.angilella@ct.infn.it>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>