Pcbnew: added: SVG plotter. Need refinements, but works.

Mainly to plot drill maps, but can be used to plot boards, for documentation.
The print svg still exists, but the plot SVG has more options (mirroring, holes in pads),
however  print svg allows color print, and full board printing, and plot does not.

common/class_bitmap_base.cpp

@@ -260,7 +260,7 @@ void BITMAP_BASE::PlotImage( PLOTTER*       aPlotter,
         return;
 
     // These 2 lines are useful only fot plotters that cannot plot a bitmap
-    // and plot arectangle instead of.
+    // and plot a rectangle instead of.
     aPlotter->SetColor( aDefaultColor );
     aPlotter->SetCurrentLineWidth( aDefaultPensize );