Silent error when uploading PNG favicon

[hdodov]

What version of GlobaLeaks are you using?

4.15.8

What browser(s) are you seeing the problem on?

All

What operating system(s) are you seeing the problem on?

macOS

Describe the issue

When you try to upload a favicon as a PNG file (many sites are like that), GlobaLeaks silently fails. There's an HTTP 403 error in the Network tab and from a UX standpoint, nothing had happened.

Proposed solution

1. PNG favicons should be allowed
2. There should be an error message if you try to upload an invalid file type
3. Allowed file types should be listed next to the upload button

[evilaliv3]

@hdodov : do you still encounter issues on 5.0.10?