fixed some issues related to user avatar

src/components/attachment/attachment.vue

src/components/chat_list_item/chat_list_item.scss

src/components/chat_title/chat_title.vue

src/components/status/status.scss

src/components/still-image/still-image.vue

src/components/user_avatar/user_avatar.vue

src/components/user_card/user_card.vue