update index for ratings/prune old entries

small stat tweaks to add players on first kill/damage event
(instead of on connect which causes issues with slow writes)

Application/Migration/DatabaseHousekeeping.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Linq;
+using IW4MAdmin.Plugins.Stats.Models;
+using SharedLibraryCore.Database;
+
+namespace IW4MAdmin.Application.Migration
+{
+    public static class DatabaseHousekeeping
+    {
+        private static DateTime _cutoffDate = DateTime.UtcNow.AddMonths(-6);
+        
+        public static void RemoveOldRatings(DatabaseContext context)
+        {
+            var dbSet = context.Set<EFRating>();
+            var itemsToDelete = dbSet.Where(rating => rating.When <= _cutoffDate);
+            dbSet.RemoveRange(itemsToDelete);
+            context.SaveChanges();
+        }
+    }
+}