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/SVG_plotter.cpp

@@ -711,7 +711,7 @@ void SVG_PLOTTER::PenTo( const VECTOR2I& pos, char plume )
 }
 
 
-bool SVG_PLOTTER::StartPlot()
+bool SVG_PLOTTER::StartPlot( const wxString& aPageNumber )
 {
     wxASSERT( m_outputFile );