Implement unknown msgtype functionality

It makes the rain look wacky.

This is a proof-of-concept example of inplementing a msgtype not found
in the spec.

Currently translated at 100.0% (942 of 942 strings)

Translated using Weblate (German)

Currently translated at 100.0% (942 of 942 strings)

Translated using Weblate (German)

Currently translated at 100.0% (942 of 942 strings)

Translated using Weblate (German)

Currently translated at 100.0% (942 of 942 strings)

Translated using Weblate (German)

Currently translated at 100.0% (942 of 942 strings)

Translated using Weblate (German)

Currently translated at 100.0% (942 of 942 strings)

Co-authored-by: Julian Groß <julian.g@posteo.de>
Co-authored-by: Mr. X <shop.news@posteo.de>
Co-authored-by: Weblate <noreply@weblate.org>
Co-authored-by: Wuzzy <Wuzzy@disroot.org>
Co-authored-by: charlie <nihil@fsfe.org>
Co-authored-by: kleines Filmröllchen <malu.bertsch@gmail.com>
Translate-URL: https://weblate.nheko.im/projects/nheko/nheko-master/de/
Translation: Nheko/nheko

Contributed by a Nheko user starting with S.

Support screen sharing with xdg-desktop-portal

Fix build on case-sensitive filesystems

Currently translated at 22.2% (210 of 942 strings)

Co-authored-by: Emilia <emilia@animegirls.info>
Translate-URL: https://weblate.nheko.im/projects/nheko/nheko-master/tr/
Translation: Nheko/nheko

Overhaul switch appearance