Helper methods extensions (#431)

* Remove unused model

* Start moving methods to extensions, cleanup code

Libraries/SPTarkov.Server.Core/Extensions/UtilityExtensions.cs

@@ -0,0 +1,13 @@
+namespace SPTarkov.Server.Core.Extensions
+{
+    public static class UtilityExtensions
+    {
+        public static List<T> IntersectWith<T>(this List<T> first, List<T> second)
+        {
+            //a.Intersect(x => b.Contains(x)).ToList();
+            // gives error Delegate type could not be infered
+
+            return first.Where(x => second.Contains(x)).ToList();
+        }
+    }
+}