Phpstan fixes

What does this MR do?

Increase the phpstan static analysis tool check level to 2 (from 0, where 10 is most verbose) and fix all upcoming issues.

For a few cases, I was actually unable to "properly" fix because I didn't get the logic, so I just went around the problem (for example for a potentially undefined variable access in quizSomething I added the check and implemented the current PHP behaviour manually)

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

Pretty sure, as it is a bunch of super small fixes.

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

changed milestone to %Release 'Birne': August 2020

added typeRefactoring label

added 1 commit

• 48c8524f - Changelog

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added 1 commit

• 1c2a73a8 - Add nullable fields to BasketService::addBasket

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approved this merge request

added 2 commits

• aad90e16 - Lower indendation level in RegionControl::index
• d1f2d249 - simplify logic in WorkGroupControl::edit

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resolved all threads

merged

added forDev label