Create other YAML files

[j0ma]

These need to be filled out manually:

• [x] conference_details.yml
• [x] sponsors.yml
• [x] prefaces.yml
• [x] organizing_committee.yml
• [x] invited_talks.yml
• [x] program.yml

Examples are available here.

Some of these need info from other organizers, as noted in #1.

[j0ma]

Work ongoing in dev branch. Currently implementing things with placeholder content.

[j0ma]

Tested compilation on branch test-compile (commit 361d224900f4f45d33a1bd986e8995dfab59bd66). Things seem to work except for paper number 8.