[synkronus] Portal - error message when upload fails

[r0ssing]

Component

• formulus (React Native mobile app)
• formulus-formplayer (React web app)
• synkronus (Go backend server)
• synkronus-cli (Command-line utility)
• Documentation
• Other (please specify)

Description

A couple of issues:

• Upload via the portal seems not to work?
• It could be refined to display a more useful error message (eg. if validation fails, the auth session has expired etc.)
• The "Auto-activate" check-box has to be checked before selecting the file, which seems counter-intuitive?