Make map legend collapsible

Closes #1196 (closed)

What does this MR do?

Adds a button above the map legend to colapse the legend to free up space on the screen.

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

It should not break things, it's almost only visual and there is only some basic css and js.

Links to related issues

From Sera Ma https://foodsharing.de/?page=bezirk&bid=734&sub=wall

How to test

1. Open the map
2. Toggle the map legend
3. Test this on different devices and screen sizes and browsers

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• used "state:" labels to track this MR's state until it was beta tested
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German

Fügt eine Schaltfläche oberhalb der Kartenlegende hinzu, um die Legende auszublenden und so Platz auf dem Bildschirm zu schaffen.