Add support to handle user blob types (negative sub type) as UDTs [JDBC358]

[firebird-automations]

Submitted by: @mrotteveel

The negative blob sub types in Firebird could be considered as UDTs (User Defined Types). Add support to read/write types implementing java.sql.SQLData (mapping to a specific subtype) reading and writing could probably be done as XDR.

TODO: More details