New SVG icons for District Map Zoom Controls

[NXXR]

Description

This fixes the map reset button of the district map to also reset the selected district to Germany (initial overview). This PR also changes the zoom buttons to use material icons for zoom in and out.

Related Issues

• 98

Checklist

I, the author of this PR checked the following requirements for good software quality:

• [x] The code is properly formatted (I ran the formatter)
• [x] The code is written with our software quality standards (I ran the linter)
• [x] The code is written using our code style
• [x] Extensive in source documentation has been added
• [x] I tried addressing all new accessibility problems displayed in the console and documented if they can't be fixed
• [x] I added the changes to the next release section of the changelog

I, the reviewer checked the following things:

• [x] I ran the software once and tried all new and related functionality to this PR
• [x] I looked at all new and changed lines of code and commented on possible problems
• [x] I read the added documentation and checked if it is understandable and clear
• [x] I checked the added tests for completeness
• [x] I checked the internationalized strings for spelling errors
• [x] I checked the performance metrics for problems or unexplained degradation
• [x] I checked that the changes are noted in the changelog

[github-actions[bot]]

Test Results

37 tests  ±0   37 :white_check_mark: ±0   12s :stopwatch: ±0s 16 suites ±0    0 :zzz: ±0   1 files   ±0    0 :x: ±0 

Results for commit 19ba1b70. ± Comparison against base commit d71d8bbf.

:recycle: This comment has been updated with latest results.