components: Honour 'prefers reduced motion' setting in many components

This helps accessibility for motion-sensitive people such as myself, and
can improve battery life in "battery saving" mode on most devices

src/components/retweet_button/retweet_button.vue

@@ -74,6 +74,9 @@
 
   .interactive {
     .svg-inline--fa {
+      @media (prefers-reduced-motion: reduce) {
+        animation: unset;
+      }
       animation-duration: 0.6s;
     }