cleanup. added fallback mechanism for IE11 and unsupported browsers.

src/App.scss

src/_variables.scss

src/components/attachment/attachment.vue

src/components/delete_button/delete_button.vue

src/components/favorite_button/favorite_button.vue

src/components/login_form/login_form.vue

src/components/nav_panel/nav_panel.vue

src/components/notifications/notifications.js

src/components/notifications/notifications.scss

src/components/notifications/notifications.vue

src/components/post_status_form/post_status_form.vue

src/components/registration/registration.vue

src/components/retweet_button/retweet_button.vue

src/components/settings/settings.vue

src/components/status/status.vue

src/components/style_switcher/style_switcher.vue

src/components/timeline/timeline.vue

src/components/user_card/user_card.vue

src/components/user_card_content/user_card_content.js

src/components/user_card_content/user_card_content.vue