Multiple improvements concerning colors, configuration handling and legacy features in pcbnew:

- support for background color setting
    - removed several global config settings (such as g_Drc_On)
    - wrapped most of global config settings in PCB_GENERAL_SETTINGS class
    - reorganized PCB general options dialog to clearly mark which options concern only the legacy canvas
    - new GAL feature for legacy users: double-click (or E) to change track width available as an option.

Fixes: lp:1530543
* https://bugs.launchpad.net/kicad/+bug/1530543

Fixes: lp:1707145
* https://bugs.launchpad.net/kicad/+bug/1707145

pcbnew/plot_brditems_plotter.cpp

@@ -56,7 +56,7 @@
 
 COLOR4D BRDITEMS_PLOTTER::getColor( LAYER_NUM aLayer )
 {
-    COLOR4D color = m_board->GetLayerColor( ToLAYER_ID( aLayer ) );
+    COLOR4D color = m_board->Colors().GetLayerColor( ToLAYER_ID( aLayer ) );
     if( color == COLOR4D::WHITE )
         color = COLOR4D( LIGHTGRAY );
     return color;
@@ -339,9 +339,11 @@ void BRDITEMS_PLOTTER::PlotDimension( DIMENSION* aDim )
     draw.SetWidth( aDim->GetWidth() );
     draw.SetLayer( aDim->GetLayer() );
 
-    COLOR4D color = getColor( aDim->GetLayer() );
+    COLOR4D color = m_board->Colors().GetLayerColor( aDim->GetLayer() );
 
-    m_plotter->SetColor( color );
+    // Set plot color (change WHITE to LIGHTGRAY because
+    // the white items are not seen on a white paper or screen
+    m_plotter->SetColor( color != WHITE ? color : LIGHTGRAY);
 
     PlotTextePcb( &aDim->Text() );