Move hypertext linking to user-page-numbers.

Also moves most navigation code to SCH_NAVIGATION_TOOL.
Also changes page number href to anchor syntax ('#foo').
Also adds hypertext processing to SCH_TEXTBOXes.
Also adds combobox with schematic pages to text properties dialog.

common/plotters/DXF_plotter.cpp

@@ -170,7 +170,7 @@ void DXF_PLOTTER::SetViewport( const VECTOR2I& aOffset, double aIusPerDecimil,
 }
 
 
-bool DXF_PLOTTER::StartPlot()
+bool DXF_PLOTTER::StartPlot( const wxString& aPageNumber )
 {
     wxASSERT( m_outputFile );