Code cleanup: remove include wx.h from pcb_plot_params.h.

including wx.h is useless for this file, and include wx.h in a lot of other files.
Include wx.h must be made only when needed in a given file, because on Windows
it include some headers that frequently create collision with kicad declarations

pcbnew/board_stackup_manager/panel_board_stackup.cpp

@@ -41,6 +41,8 @@
 #include "dialog_dielectric_list_manager.h"
 #include <wx/wupdlock.h>
 #include <wx/richmsgdlg.h>
+#include <wx/choicdlg.h>
+#include <wx/dcclient.h>
 
 // Some wx widget ID to know what widget has fired a event:
 #define ID_INCREMENT 256    // space between 2 ID type. Bigger than the layer count max

pcbnew/dialogs/panel_setup_layers.cpp

@@ -33,6 +33,8 @@
 #include <collectors.h>
 #include <panel_setup_layers.h>
 
+#include <wx/choicdlg.h>
+
 
 // some define to choose how copper layers widgets are shown
 

pcbnew/exporters/export_gencad.cpp

@@ -44,6 +44,8 @@
 #include <pgm_base.h>
 #include <project/project_file.h> // LAST_PATH_TYPE
 
+#include <wx/app.h>
+
 static bool CreateHeaderInfoData( FILE* aFile, PCB_EDIT_FRAME* frame );
 static void CreateArtworksSection( FILE* aFile );
 static void CreateTracksInfoData( FILE* aFile, BOARD* aPcb );

pcbnew/pcb_layer_box_selector.cpp

@@ -36,6 +36,8 @@
 #include <pcb_layer_box_selector.h>
 #include <tools/pcb_actions.h>
 
+#include <wx/dcclient.h>
+
 // translate aLayer to its hotkey
 static TOOL_ACTION* layer2action( PCB_LAYER_ID aLayer )
 {

pcbnew/pcb_plot_params.h

@@ -3,7 +3,7 @@
 /*
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
- * Copyright (C) 1992-2018 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 1992-2021 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -23,7 +23,6 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  */
 
-#include <wx/wx.h>
 #include <outline_mode.h>
 #include <plotter.h>
 #include <layers_id_colors_and_visibility.h>

pcbnew/widgets/appearance_controls.h

@@ -38,6 +38,8 @@ class ROW_ICON_PROVIDER;
 class GRID_BITMAP_TOGGLE_RENDERER;
 class WX_COLLAPSIBLE_PANE;
 class wxStaticLine;
+class wxSlider;
+class wxRadioButton;
 
 using KIGFX::COLOR4D;