Main form GUI tweaks (#1804)

- Added Expand All Nodes menu
- Added Collapse All Nodes menu

Author: sindizzy

LibreHardwareMonitor/UI/Gadget.cs

@@ -175,4 +175,4 @@ public void Redraw()
     }
 
     protected abstract void OnPaint(PaintEventArgs e);
-}
+}

LibreHardwareMonitor/UI/MainForm.Designer.cs

@@ -1239,6 +1239,16 @@ private void ResetMinMaxMenuItem_Click(object sender, EventArgs e)
         }));
     }
 
+    private void ExpandAllNodes_Click(object sender, EventArgs e)
+    {
+        treeView.ExpandAll();
+    }
+
+    private void CollapsepAllNodes_Click(object sender, EventArgs e)
+    {
+        treeView.CollapseAll();
+    }
+
     private void resetPlotMenuItem_Click(object sender, EventArgs e)
     {
         _computer.Accept(new SensorVisitor(delegate (ISensor sensorClick)