refactored wakeupSleepingUsers in MaintenanceControl to Gateway

Closes None

What does this MR do?

The wakeupSleepingUsers() is refactored to the newer db function and to the gatewayclass.

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

It works locally.

Links to related issues

It has something to do with this: #9 (closed)

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. don't forget ./scripts/start and ./scripts/seed
3. set a time of being unavailable for a foodsaver to be until today
4. run ./scripts/docker-compose run --rm --no-deps app php -f run.php Maintenance daily
5. check if the foodsaver is available again

Screenshots (if applicable)

Any relevant screenshots if this is a design / frontend change

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))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings