Unified pickup logic
What does this MR do?
Pull out common pickup logic into the StoreService. This also needs a bit of frontend change as currently backend/frontend logic are quite intertwined...
This also fixes a bug (currently on production) where the backend allows users to signup for already taken pickups in case there is another single pickup in the store available.
How confident are you it won't break things if deployed?
Links to related issues
- 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))