Fixed Wikipedia workload for Oracle

- WikipediaLoader: Some randomly created data raised ORA-1400 (inserting NULL
values into NOT NULL columns). This has to do with how Oracle handles empty
strings.
- SQL: Also, Oracle handles double quotes differently. If a table is defined as
'"useracct"' (with double quotes), then all other operations also have to use
double quotes in the table identifier, otherwise you'll get "ORA-00942: table
or view does not exist".
- SQL: Still working on optimizing the Triggers