Add button loading state

src/components/input/button.vue

@@ -2,6 +2,7 @@
     <a 
         class="button" 
         :class="{
+            'is-loading': loading,
             'is-primary': type === 'primary',
             'is-outlined': type === 'secondary',
             'is-text is-inverted has-no-shadow underline-none': type === 'tertary',
@@ -25,6 +26,10 @@ export default {
             type: String,
             default: '',
         },
+        loading: {
+            type: Boolean,
+            default: false,
+        },
     },
 }
 </script>