New data model migration for users, bookmarks and playback sessions

server/objects/metadata/BookMetadata.js

@@ -46,7 +46,7 @@ class BookMetadata {
       subtitle: this.subtitle,
       authors: this.authors.map(a => ({ ...a })), // Author JSONMinimal with name and id
       narrators: [...this.narrators],
-      series: this.series.map(s => ({ ...s })),
+      series: this.series.map(s => ({ ...s })), // Series JSONMinimal with name, id and sequence
       genres: [...this.genres],
       publishedYear: this.publishedYear,
       publishedDate: this.publishedDate,
@@ -80,6 +80,10 @@ class BookMetadata {
     }
   }
 
+  clone() {
+    return new BookMetadata(this.toJSON())
+  }
+
   get titleIgnorePrefix() {
     if (!this.title) return ''
     if (this.title.toLowerCase().startsWith('the ')) {