Add topbar dropdown menu (#937)

* Add basic menu

* Add workflows/edit to menu bar

* Add command store

* Fix z-index

* Fix beta menu setting switch

* nit

* Drop to center

* Fix command invocation

src/assets/css/style.css

@@ -82,7 +82,8 @@ body {
   grid-column: 1/-1;
   /* Position at the first row */
   grid-row: 1;
-  z-index: 10;
+  /* Top menu bar dropdown needs to be above of graph canvas splitter overlay which is z-index: 999 */
+  z-index: 1000;
   display: flex;
   flex-direction: column;
 }