Fix earlier commit + GStreamer v1.18 released

Added emoji completion in text input

Link GStreamer elements before syncing state

New event store

The loss in durability shouldn't matter, if we can just receive the same
events again after a restart

Under GStreamer >= 1.17 gather all candidates before sending offer/answer

Add nixos to readme

Stop SendFile and Call buttons swapping places on file upload

Conflicts:
	CMakeLists.txt
	io.github.NhekoReborn.Nheko.json
	src/Cache.cpp
	src/timeline/TimelineModel.cpp
	src/timeline/TimelineModel.h
	src/timeline/TimelineViewManager.cpp

Currently translated at 85.3% (285 of 334 strings)

Translation: Nheko/nheko
Translate-URL: http://weblate.nheko.im/projects/nheko/nheko-master/en/

Support voice calls

Integrating that in our CI is currently a bit hard, so disable it for
now, if GStreamer isn't found. Just make sure to build against GStreamer
for call support!