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/Activity/Queue/QueueRow.js

@@ -321,6 +321,8 @@ class QueueRow extends Component {
           downloadId={downloadId}
           title={title}
           onModalClose={this.onInteractiveImportModalClose}
+          showReplaceExistingFiles={true}
+          replaceExistingFiles={true}
         />
 
         <RemoveQueueItemModal