WIP: auto-confirm for stores

Closes #406

What does this MR do?

still work in progress

How confident are you it won't break things if deployed?

meh

SQL migration script

ALTER TABLE `fs_betrieb` ADD `slot_autoconfirm` BIT NOT NULL DEFAULT 0 AFTER `abholmenge`;

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))