Add more twig templating

What does this MR do?

Implements the main menu via twig templating and some other smaller things.

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

I wouldn't be surprised if something breaks, but I did my best, added tests and all...

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))