Add AutomationCommands class

- AutomationCommands replaces GetAllMenuCommands, and can provide
information about menus, buttons and toolbars to a script.
- BatchCommands can now return textual results to a script.
- There's a new GUID for mod-script-pipe and it is included in the .sln.

src/BatchCommands.cpp

@@ -70,6 +70,7 @@ static const wxString MP3Conversion = wxT("MP3 Conversion");
 
 BatchCommands::BatchCommands()
 {
+   mMessage = "";
    ResetChain();
 
    wxArrayString names = GetNames();