Merge branch 'appearance-tab' into 'develop'

changelog.d/appearance-tab.change

changelog.d/emoji-scale.add

changelog.d/firefox-redmon.fix

changelog.d/theme-selector.add

changelog.d/ui-scale.add

changelog.d/user-overrides.add

preview.style.js

src/App.scss

src/boot/after_store.js

src/components/emoji_picker/emoji_picker.js

src/components/emoji_picker/emoji_picker.scss

src/components/emoji_reactions/emoji_reactions.vue

src/components/font_control/font_control.js

src/components/font_control/font_control.vue

src/components/mobile_nav/mobile_nav.vue

src/components/navigation/navigation_pins.vue

src/components/notification/notification.style.js

src/components/panel.style.js

src/components/root.style.js

src/components/settings_modal/helpers/number_setting.vue