Functions to add a blank page

[enriquehdez98]

System Information:

• 3D Slicer 5.10.0
• Windows 10
• Tutorial Maker — develop branch (version downloaded on 11/19/25 at 11:00 AM)

Issue description:
The function to add blank pages was lost; this allowed the user to add slides with text and titles only.

[LuskasHusty]

@enriquehdez98 do you mean the blank page that can be added via the gallery?

Maybe some placeholder text should be added to the blank slide.