feat(Layout): add loading spinner component and to layout

Reusable spinner component

Apply spinner to layout to show a "loading state" between transitions, the spinner only shows if the transition is taking more than .2 secconds

src/assets/style/global.css

@@ -102,3 +102,7 @@ li:not(:last-child) {
     height: 100% !important;
   }
 }
+
+.d-none {
+  display: none;
+}