Adjust margins on home page, globally fix hr elements to default to having margins, and add class for hr elements to span full width of their container

styles/core/_util.scss

@@ -88,5 +88,9 @@ p {
 hr {
   border: 0;
   border-bottom: 1px solid $color-gray-light;
-  margin: ($gap * 3) ($site-margins * -4);
+  margin: ($gap * 3) 0;
+
+  &.full-width {
+    margin: ($gap * 3) ($site-margins * -4);
+  }
 }