Allow orga-files/folders to be accessible in meetings

[Elblinator]

Desired behaviour:

• An Orgaadmin and superadmin should be able to set files or whole folders onto the status „public“, public folders/files are displayed in every meeting.
• These global/public files/folders should not be deletable from a meeting
• These files/folders should be in a meeting per default only visible for the admin group. Per default means: if a new meeting is created or a new folder/file is created/uploaded
• The folder/file should have an icon as indicator to show that they are public in every meeting, I would recommend the „Public“ icon until further notice. -> This icon should be visible on the orga- and the meeting-level

[Elblinator]

waiting for
OpenSlides/openslides-backend#2499
OpenSlides/openslides-meta#121