Use utf8mb4

Closes #338 (closed)

What does this MR do?

We need to switch the database to use utf8mb4 instead of utf8 (which is utf8mb3).

This changes everything to utf8mb4. I think I got most of the things set... I also added tests that showed the error happening, and it being resolved.

I needed to update three seperate database configurations:

• the legacy mysqli
• the new PDO
• the test PDO

There is a test for all of them now :) - and an API test to test the whole thing. And it works in my local machine dev setup.

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

Good chance something will break :) Will sit with Matthias late at night putting it all right probably.

The database changes might take some time to run. Maybe we need to take the site offline for a while, etc...

Links to related issues

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))