New: Manual import improvements (#683)

* New: Manual import improvements

 - Detect and merge import with files already in library.
 - Allow selection of album release from Manual Import modal.
 - Loading indicator while fetching updated decisions

* Disable release switching if user manually overrode release

frontend/src/Components/SignalRConnector.js

@@ -229,16 +229,6 @@ class SignalRConnector extends Component {
     }
   }
 
-  handleManualimport = (body) => {
-    if (body.action === 'updated') {
-      this.props.dispatchUpdateItem({
-        section: 'interactiveImport',
-        updateOnly: true,
-        ...body.resource
-      });
-    }
-  }
-
   handleQueue = () => {
     if (this.props.isQueuePopulated) {
       this.props.dispatchFetchQueue();