Modified the program so that each tree view may have correct view
with corresponding document page when multi drawings are opened.
For this purpose activePage must be replaced by the page where treeview window is open.
ActiveWindow.ID is passed from button1_Click in Ribbon.cs via AnchorBarUsage.cs to Form1.cs.
All ActivePage in Form1.cs are replaced to visioActivePage.
visioActivePage = app.Windows.get_ItemFromID(visiowindowID).Page.
And please, save Ribbon designer once before run the project.