UI adjustments to photo upload flow

[spwoodcock]

1. Move the button to upload the modal

The button should be more prominent.
It should be larger and very clear to the user.
Centralise with the sidebar UI on the left.

2. User error: can continue before batch processed

• It's possible to click continue before the whole batch is processed.
• We should definitely only enable the continue button after they are all done.
• When I continue, then I can't go back, as it makes me abort the process. I don't think all the images were processed when I click continue though.

3. It's possible to continue, before the images are classified

• Clicking the 'Classify' button seems to be optional currently.
• It should be a mandatory step, so the user can't continue unless they have classified imagery.

[linear]

TECH-956

[spwoodcock]

@FeezyHendrix I think @konishon made a start on this in his draft PR - have you already solved it, or would it be best to work on another issue? 🙏 Thanks both for your support!!