Remove property.h and property_mgr.h from inspectable.h

This breaks the view_item.h -> inspectable.h -> property.h chain that
pulled wx/propgrid/property.h into 150-200 TUs. The lean inspectable.h
now includes only wx/any.h, wx/string.h, wx/variant.h.

Headers using DECLARE_ENUM_TO_WXANY (board_item.h, sch_item.h) retain
their property.h include since the macro requires it.

pcbnew/python/scripting/pcbnew_scripting_helpers.cpp

@@ -61,6 +61,8 @@
 #include <wx/app.h>
 #include <wx/crt.h>
 #include <wx/image.h>
+#include <properties/property.h>
+#include <properties/property_mgr.h>
 
 static PCB_EDIT_FRAME* s_PcbEditFrame = nullptr;
 static SETTINGS_MANAGER* s_SettingsManager = nullptr;