Preparing for the History query

WotBlitzStatisticsPro.Common/Model/StatisticsDifferenceItem.cs

@@ -0,0 +1,18 @@
+namespace WotBlitzStatisticsPro.Common.Model
+{
+    /// <summary>
+    /// Represents the difference of one statistics parameter
+    /// </summary>
+    public class StatisticsDifferenceItem<T> where T: struct
+    {
+        /// <summary>
+        /// The current value of statistics item
+        /// </summary>
+        public T CurrentValue { get; set; }
+
+        /// <summary>
+        /// The difference between current and previous value
+        /// </summary>
+        public T? Difference { get; set; }
+    }
+}