Exclude dev/debug classes from DI

Production does not install dev dependencies which are used in the SeedCommand inside the Foodsharing\Dev namespace.

Also, we might only want DI for actual modules for now.

• 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))