chat: Disable asynchronous image loading

The problem is currently that not all images are displayed when
asynchronous loading is on.
8 jobs for release/v0.4.0 in 8 minutes and 39 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #2258
clazy

00:03:17

passed #2259
qmllint

00:03:09

 
  Build
passed #2263
archlinux

00:01:21

passed #2262
debian-sid

00:02:17

passed #2261
neon-bionic

00:01:29

passed #2260
ubuntu-trusty

00:02:18

 
  Deploy
passed #2265
click-xenial

00:02:30

passed #2264
linux-appimage

00:02:20