[1115725] Operation history continues to grow unbound with no easy way to purge old history
Add operation history purge to the data purge job.  A new system setting
is added with a default of 0 days, which means disabled. The db-upgrade
will add the new setting, also set to 0=disabled so that upgrades don't
automatically force an unexpected purge of operation history.
Also:
- cleaned up some I18N when adding the new properties, removing some
  duplicates, adding commented, missing translations, etc. Some touched
  files were only due to some remvals of deuplicate I18N properties.
- added DatabaseType.getLimitClause() although in the end I didn't use it.