Add footprint select dropdown to component chooser, serious refactoring

- DIALOG_CHOOSE_COMPONENT has footprint select widget
- FOOTPRINT_SELECT_WIDGET
- FOOTPRINT_CHOICE widget (customized wxComboCtrl)
- FOOTPRINT_FILTER class
- FOOTPRINT_INFO rework:
    - FOOTPRINT_ASYNC_LOADER to load without freezing UI
    - Rewrite loader threads as queue-driven thread pool
    - Make FOOTPRINT_INFO available via kiway
- FP_LIB_TABLE::PrefetchLib
- Access to global fp-lib-table via kiway
- SYNC_QUEUE threadsafe queue template
- Remove KICAD_FOOTPRINT_SELECTOR build option

pcbnew/plugin.cpp

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2011-2012 SoftPLC Corporation, Dick Hollenbeck <[email protected]>
- * Copyright (C) 2016 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 2016-2017 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
@@ -66,6 +66,13 @@ wxArrayString PLUGIN::FootprintEnumerate( const wxString& aLibraryPath, const PR
 }
 
 
+void PLUGIN::PrefetchLib( const wxString& aLibraryPath, const PROPERTIES* aProperties )
+{
+    (void) aLibraryPath;
+    (void) aProperties;
+}
+
+
 MODULE* PLUGIN::FootprintLoad( const wxString& aLibraryPath, const wxString& aFootprintName,
                                     const PROPERTIES* aProperties )
 {