Use Material style for all platforms

The Material style is now used on all platforms. This makes styling the
app much more easy, as we do not have to deal with color schemes e.g.
with the Fusion style.

Support for other styles might be added back in the future, but for now
it is better to concentrate on one style only.
12 jobs for 188-switch-to-material-theme-for-all-platforms in 51 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Images
manual #56357481
allowed to fail manual
build_image_android
manual #56357478
allowed to fail manual
build_image_ubuntu
manual #56357479
allowed to fail manual
build_image_win32
manual #56357480
allowed to fail manual
build_image_win64
 
  Build
passed #56357488
android_armv7

00:09:13

passed #56357489
android_x86

00:09:58

manual #56357487
macos allowed to fail manual
macos
passed #56357482
ubuntu_appimage

00:51:15

passed #56357483
win32_build

00:07:07

manual #56357485
windows allowed to fail manual
win32_vs_build
passed #56357484
win64_build

00:07:21

manual #56357486
windows allowed to fail manual
win64_vs_build