Lots of changes to get code ready to add library.

API/Entities/Library.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace API.Entities
+{
+    public class Library
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+        public string CoverImage { get; set; }
+        public LibraryType Type { get; set; }
+        public ICollection<FolderPath> Folders { get; set; }
+        
+        public AppUser AppUser { get; set; }
+        public int AppUserId { get; set; }
+    }
+}