Fix fairteiler email notification can be triggered by anyone
What does this MR do?
- removes wallpostReady client side callback
- removes basket follower functionality (which did nothing except a DB entry)
- move fairteiler new wallpost notification trigger into backend
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))