Add red frame around observation on uploader when it is incomplete

[pisum]

i think this is more or less the same thing as: https://forum.inaturalist.org/t/missing-something-pop-ups-in-web-up-loader-should-also-highlight-observations-that-triggered-them/30373.

my response there, which i think is relevant here, was:

@pisum

i think any implementation should done in a way that it does not suggest that fields are required (as opposed to just recommended) or that there’s an error (as opposed to just a warning or information).