Speaker images on conference page are broken

[straight-shoota]

They are pulled directly from airtable which is broken somehow.

It's probably best to track the images in Airtable and put them in the repo to be future proof. And then replace the URLs in master/_data/conference_talks.csv.

Alterantively we could also collect the images anew (from GitHub avatars etc.) if Airtable does not work out.