Replace fetch by axios

[fschmenger]

This is a proposed cleanup task by @JakobMiksch from #269. The Fetch API is replaced by axios, no functional changes.

[fschmenger]

Please re-run the tests after #269 has been merged, as I didn't include the axios package here again to avoid conflicts (already included in #269).

Open task:
I didn't dare to touch the geocoder requests, those already have been marked with.
https://github.com/meggsimum/wegue/blob/abb2b3518d54b0390ffefe765e0c568122631448/src/components/geocoder/helpers/ajax.js#L24

As far as I can see, the involved JSONP requests require a separate JsonP adapter. However from looking at the providers, none is currently configured to use JSONP, so the corresponding code might as well be deprecated.
Since I'm not familiar with all the geocoder provider specs and I didn't have the time to go through dozens of tests, I'll leave this for later.

[JakobMiksch]

Thanks for the fix. I will merge.