Badly chosen new version flag implementation for upload image

[ValentijnvdBeek]

Summary

Since there are now multiple image types, there are some for which versions make sense and some for which they do not. This means that when you are uploading an image you may want to either create a new version, update the checksum or neither. The current implementation sets a boolean flag as a mulitpart section which is rather weird and clunky.

Proposed fix

Use a HTTP header instead or, alternative, create a separate endpoint.