Resolve "Change contact methods"

Closes #1104

See merge request !1820

(cherry picked from commit ec190fde)

f53d2777 removed direct mail option
34ed8a16 switched mail adress
695af99e Added possibility to attach files to message
5623cdd6 file upload and validation working properly
f3d30689 removed E-Mail Adresses from team website
9a9b216a replaced every mention of email adress with a link to contact form
69476f8a fixed dockerfile
8b2e8dbc attachments are now optional
ffcb7163 increased ingress body size