new command «certificate» to install CA certificate for SSL

src/commands.hxx

@@ -1409,7 +1409,7 @@ class Certificate: public Command {
         "Load a CA certificate that will be accepted on SSL connections.";
     }
     QString command() const {
-      return "";
+      return "certificate "+_filename;
     }
     std::shared_ptr<Command> parse(Script*, QString args,
                                    QStringList&, int) {