190607 c1

- Add Pilz.Drawing.Drawing3D.OpenGLFactory
- Fix small bugs in Pilz.UI.PaintingControl

Pilz.Collections/SimpleHistory/SimpleHistory.vb

@@ -7,6 +7,16 @@ Namespace SimpleHistory
         Private stackPast As New Stack(Of HistoryPoint)
         Private stackFuture As New Stack(Of HistoryPoint)
 
+        ''' <summary>
+        ''' Gets the count of history points.
+        ''' </summary>
+        ''' <returns></returns>
+        Public ReadOnly Property ChangesCount As Boolean
+            Get
+                Return stackPast.Count
+            End Get
+        End Property
+
         ''' <summary>
         ''' Checks if the History has past changes.
         ''' </summary>