revert to VB and update to new project file format

Pilz.Simple3DFileParser/Model/ModelBoundaries.vb

@@ -0,0 +1,11 @@
+Imports System.Numerics
+
+Public Class ModelBoundaries
+    Public ReadOnly Upper As Vector3
+    Public ReadOnly Lower As Vector3
+
+    Public Sub New(upper As Vector3, lower As Vector3)
+        Me.Upper = upper
+        Me.Lower = lower
+    End Sub
+End Class