Draft: HTTP errors handeling

This MR addresses any http error while using the remote servers (Plate solving, PCC, search, solsys).

The goal is to give the user a few more information on "what's not going on".

For test purpose only, a fake url (https://httpstat.us/random/500-504) is hard-coded.

Nor siril-update or more details... (in quick PSF) is concerned.