Allow select/unselect by sections when photos are rendered by sections

[artonge]

Describe the solution you'd like

• [ ] Once you selected one photo, a checkbox can appear on the left of each section heading as well. This would allow you to select and unselect an entire month, for example.
• [ ] Once you select a photo, there could also be an "X Cancel" button on the right corner of the header which would unselect all.
• [ ] Additionally: show the number of items selected on the left of the button in the header. Eg. "15 items selected"
• [ ] Select new loaded items if section is selected
• [ ] Not loaded items should be checked on favorite, delete, ...