Add missing items to changelog (clean url tester, sticky table header) and group related items together.

- Patch #67893 by kbahey, dww, alienbrain, asimmonds et al: made it possible to filter log messages in the database log.

- Patch #63881 by kbahey and jakeg: improved Drupal's logging functionality.  Added support for external loggers, and included a small syslog module into core.

- Refactor partial-page handling for the maintenance page. It's an exotic quirk for update.php and belongs there.

- Patch #59863 by sun et al: added a scripts/drupal.sh to execute Drupal code from the command line.  This is great for using Drupal as a scripting framework, or to write backup or migration scripts.

- Updated CHANGELOG.