Feature/pt fix sql concatenation in gateways

What does this MR do?

removes sql injection possibilities from all already existing gateways.

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

Quite. It is only refactoring and tests pass.

Checklist

• added a test, or explain why one is not needed/possible... (no new functi.)
• 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))