Expose grid axes color control

Note: axis thickness is currently calculated from grid line
thickness.  I'm not adding a separate control for it as
requested in the original issue right now, but if we determine
that we need a separate control it can be added.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/2353

pcbnew/dialogs/panel_modedit_color_settings.cpp

@@ -65,7 +65,6 @@ PANEL_MODEDIT_COLOR_SETTINGS::PANEL_MODEDIT_COLOR_SETTINGS( FOOTPRINT_EDIT_FRAME
     for( int id = GAL_LAYER_ID_START; id < GAL_LAYER_ID_END; id++ )
     {
         if( id == LAYER_VIAS
-         || id == LAYER_GRID_AXES
          || id == LAYER_PADS_PLATEDHOLES
          || id == LAYER_VIAS_HOLES )
         {

pcbnew/dialogs/panel_pcbnew_color_settings.cpp

@@ -354,7 +354,6 @@ std::string g_previewBoard =
 std::set<int> g_excludedLayers =
         {
             LAYER_VIAS,
-            LAYER_GRID_AXES,
             LAYER_MOD_FR,
             LAYER_MOD_BK,
             LAYER_MOD_VALUES,

pcbnew/pcb_draw_panel_gal.cpp

@@ -251,6 +251,7 @@ void PCB_DRAW_PANEL_GAL::UpdateColors()
     rs->LoadColors( cs );
 
     m_gal->SetGridColor( cs->GetColor( LAYER_GRID ) );
+    m_gal->SetAxesColor( cs->GetColor( LAYER_GRID_AXES ) );
     m_gal->SetCursorColor( cs->GetColor( LAYER_CURSOR ) );
 }