fix issue when used with importmap as DomContentLoaded is fired twice when using es shims module

Author: jonasjabari

lib/matestack/ui/vue_js/index.js

@@ -1,3 +1,4 @@
+import axios from 'axios'
 import eventHub from './event_hub'
 const matestackEventHub = eventHub // for compatibility with 1.x
 
@@ -68,14 +69,18 @@ const registerComponents = function(appInstance){
 }
 
 const mount = function(appInstance, elementId='#matestack-ui'){
-  registerComponents(appInstance)
+  if (window.matestackAppMounted != true){
+    window.matestackAppMounted = true
+    registerComponents(appInstance)
 
-  appInstance.mount(elementId)
+    appInstance.mount(elementId)
+  }
 
   return appInstance
 }
 
 const MatestackUiVueJs = {
+  axios,
   eventHub,
   matestackEventHub, // for compatibility with 1.x
   componentMixin,