First pass at cleaning entity classes.

- Documents all library entities
- Fixes styling warnings for library entities
- Updates library entities to inherit from interfaces
- Makes library entites no longer partial.

Jellyfin.Data/Entities/User.cs

@@ -8,13 +8,14 @@ using System.Globalization;
 using System.Linq;
 using System.Text.Json.Serialization;
 using Jellyfin.Data.Enums;
+using Jellyfin.Data.Interfaces;
 
 namespace Jellyfin.Data.Entities
 {
     /// <summary>
     /// An entity representing a user.
     /// </summary>
-    public partial class User : IHasPermissions, ISavingChanges
+    public partial class User : IHasPermissions, IHasConcurrencyToken
     {
         /// <summary>
         /// The values being delimited here are Guids, so commas work as they do not appear in Guids.