set default elo rating

maybe fix deadlock again :c
changed "skill" to Performance (Skill + Elo / 2)

SharedLibraryCore/Migrations/20180517223349_AddRollingKDR.cs

@@ -0,0 +1,25 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+using System;
+using System.Collections.Generic;
+
+namespace SharedLibraryCore.Migrations
+{
+    public partial class AddRollingKDR : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<double>(
+                name: "RollingWeightedKDR",
+                table: "EFClientStatistics",
+                nullable: false,
+                defaultValue: 0.0);
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "RollingWeightedKDR",
+                table: "EFClientStatistics");
+        }
+    }
+}