Rename element list classes to singular and use them in examples (#2853)

core/scss/ui/_badges.scss

@@ -70,9 +70,11 @@
 }
 
 //
-// Badges list
+// Badge list
 //
+.badge-list,
 .badges-list {
+  // `.badges-list` is deprecated, use `.badge-list` instead
   @include elements-list();
 }
 

core/scss/ui/_tags.scss

@@ -66,8 +66,10 @@
 }
 
 //
-// Tags list
+// Tag list
 //
+.tag-list,
 .tags-list {
+  // `.tags-list` is deprecated, use `.tag-list` instead
   @include elements-list();
 }