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.

include/plotters/plotter.h

@@ -123,7 +123,7 @@ public:
      */
     virtual PLOT_FORMAT GetPlotterType() const = 0;
 
-    virtual bool StartPlot() = 0;
+    virtual bool StartPlot( const wxString& aPageNumber ) = 0;
     virtual bool EndPlot() = 0;
 
     virtual void SetNegative( bool aNegative ) { m_negativeMode = aNegative; }