Maintenance of forum reading count feature
- removal of forums_reading_info_user (1Mio rows on Learn@WU).
This materialized view had to be constantly synced with
forums_reading_info table. Reimplemented as view.
- simplify logics in stored procedure due to new datamodel
- fix inconsistencies between oracle and postgres function definition
- re-enabled parameter to decide whether use these stats or not in
administration
TODO: consider further reform of this feature as stats grow very
large on busy sites for probably little value added
