Upload button on mobile should display warning/info

[lourot]

Since https://frameright.app works only on desktop, it is unlikely that, as of today, the user will have pictures with Image Regions on their phone. Thus when clicking on Upload on their phone, we should tell them to better switch to desktop for now.

[ilu]

I would keep the behavior as is. I think it is an excellent demo if a person has been able to move an image with IDC metadata onto their phone, even if they have not created it on that device. We could show them a message on mobile guiding them to create the IDC metadata on desktop but still have the possibility to upload on mobile too.

[lourot]

After chatting with @MarinaEkroos, let's think about it more. If it's hard to transfer images to a phone without losing metadata at the moment, we might as well remove the Upload button on mobile and replace it with a third picture.