Add simple class-specific bookmarks view

[#75129758]

Bookmarks still don't have class_id field, so for now this view
lists all the bookmarks.
Add clazz_id to Bookmarks, filter bookmarks by class in class view

[#75129758]
Remove old bookmarks UI

[#75129758]
Add let author create padlet in class view

[#75129758]

WIP
Implement new bookmarks UI, handle per-class generic bookmarks creation

[#75129758]
Try to make links UI more consistent

[#75129758]

Every form used to look different and so on.