No way to clear all checkboxes in backup schema settings

In Moodle 1.9, when performing a backup of a large course, it was possible to clear all the checkboxes by clicking the "Include all/none" box. This made it easy to create a backup containing just a few resources.

In Moodle 2.2, the equivalent form is "Schema settings" in backup, and this does not have a facility to clear the checkboxes. This means they have to be cleared one by one, a tedious process when the course is large.

Restoring the include all/none feature would be an improvement.

Steps to reproduce
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1. Find an existing course containing many resources and activities.
2. Click Backup
3. On Backup settings form, select "Include activities" and "Include enrolled users".
4. On Schema settings form, try to include only the announcements forum and its user data in the backup. It can only be done by manually unchecking every single other box.