Merge branch 'mergeback-master' into 'develop'

changelog.d/themes3-cache.add

changelog.d/themes3-fixes.fix

changelog.d/themes3.change

changelog.d/themesv3-on-safari.fix

changelog.d/ui-scale.add

changelog.d/unreads-sync.fix

changelog.d/user-overrides.add

changelog.d/video-poster.fix

changelog.d/video-poster.update.skip

changelog.d/web-push-always.add

package.json

src/boot/after_store.js

src/components/emoji_picker/emoji_picker.js

src/components/emoji_picker/emoji_picker.vue

src/components/timeline/timeline.scss

src/services/theme_data/theme2_to_theme3.js