Add libraries for EntityFramework

Stats plugin work
Allow plugins to dynamically add EF classes to the context

Plugins/SimpleStats/Models/EFClientStatistics.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using SharedLibrary.Database.Models;
+
+namespace StatsPlugin.Models
+{
+    public class EFClientStatistics : SharedEntity
+    {
+        [Key, Column(Order = 0)]
+        public int ClientId { get; set; }
+        [ForeignKey("ClientId")]
+        public virtual EFClient Client { get; set; }
+        [Key, Column(Order = 1)]
+        public int ServerId { get; set; }
+        [ForeignKey("ServerId")]
+        public virtual EFServer Server { get; set; }
+        [Required]
+        public int Kills { get; set; }
+        [Required]
+        public int Deaths { get; set; }
+        [Required]
+        [NotMapped]
+        public double KDR
+        {
+            get => Deaths == 0 ? 0.0 : Math.Round((float)Kills / (float)Deaths, 2);
+        }
+        [Required]
+        public double SPM { get; set; }
+        [Required]
+        public double Skill { get; set; }
+    }
+}