Blackboad Item Heading apparently not working with hidden items

[djplaner]

Indications are that sections with Blackboard Item Headings aren't disappearing when the matching item is unavailable. Test and fix.

Perhaps also update messaging in these situations?

[djplaner]

Having to do a complete re-write of handleBlackboardItem

Testing

• [x] review status with com12 is working - editModeOff
• [x] review status with com12 is working - editModeOn
• [x] media relations hiding h1 section
• [x] media relations hiding h2 section
• [x] no matching item
• [x] more than one matching item
• [ ] update documentation
• [ ] Including noHiddenSections parameter