Add optional project parameter to PCB plugin load method.

The optional PROJECT parameter is primarily used for third party plugins
that need to store project information loaded by the plugin.

pcbnew/plugins/pcad/pcad_plugin.cpp

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2012 Alexander Lunev <[email protected]>
- * Copyright (C) 2012 KiCad Developers, see CHANGELOG.TXT for contributors.
+ * Copyright (C) 2012-2020 KiCad Developers, see CHANGELOG.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
@@ -64,7 +64,8 @@ const wxString PCAD_PLUGIN::GetFileExtension() const
 }
 
 
-BOARD* PCAD_PLUGIN::Load( const wxString& aFileName, BOARD* aAppendToMe, const PROPERTIES* aProperties )
+BOARD* PCAD_PLUGIN::Load( const wxString& aFileName, BOARD* aAppendToMe,
+                          const PROPERTIES* aProperties, PROJECT* aProject )
 {
     wxXmlDocument   xmlDoc;