Implement benchmark in GUI.

DiscImageChef.Gui/Forms/frmMain.xeto

@@ -51,6 +51,7 @@
                 <ButtonMenuItem Text="&amp;Console" Click="OnMenuConsole"/>
             </ButtonMenuItem>
             <ButtonMenuItem Text="&amp;Help">
+                <ButtonMenuItem Text="&amp;Benchmark" Click="OnMenuBenchmark"/>
                 <ButtonMenuItem Text="&amp;Encodings" Click="OnMenuEncodings"/>
                 <ButtonMenuItem Text="&amp;Plugins" Click="OnMenuPlugins"/>
             </ButtonMenuItem>

DiscImageChef.Gui/Forms/frmMain.xeto.cs

@@ -473,6 +473,11 @@ namespace DiscImageChef.Gui.Forms
             new dlgEncodings().ShowModal(this);
         }
 
+        protected void OnMenuBenchmark(object sender, EventArgs e)
+        {
+            new dlgBenchmark().ShowModal(this);
+        }
+
         protected void OnTreeImagesSelectedItemChanged(object sender, EventArgs e)
         {
             if(!(sender is TreeGridView tree)) return;