dispose substance drag manage to let react dnd to work

app/components/SimpleEditor/Editor.js

@@ -275,6 +275,10 @@ class Editor extends ProseEditor {
       trackChangesProvider
     }
   }
+
+  dispose () {
+    this.editorSession.dragManager.dispose()
+  }
 }
 
 export default Editor

app/components/SimpleEditor/SimpleEditor.jsx

@@ -152,7 +152,7 @@ export default class SimpleEditor extends React.Component {
       config: configurator.config
     })
 
-    Editor.mount({
+    this.editor = Editor.mount({
       book,
       configurator,
       containerId,
@@ -174,6 +174,8 @@ export default class SimpleEditor extends React.Component {
   componentWillUnmount () {
     this._releaseLock()
     window.removeEventListener('beforeunload', this._releaseLock)
+
+    this.editor.dispose()
   }
 
   // TODO -- use this for correctly refreshing props when the fragment arrives