Upload member related documents

[Viko1690]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
For example: Everyone who wants to get a member have to fill out some membership declaration (we actually don‘t use the sign in functionality of admidio). It would be nice to upload a scan of the declaration and store it in the member profile. Also storing other user related documents like letters would be helpful.

Admidio is a very nice tool and I love to use it. Thank you for the great work!