Command injection by setting a custom search engine

**Summary:** Arbitrary commands can be injected when using the "Search on Internet" function with a malicious custom search engine. The custom search engine can be set through the GUI or the config files, with different attack scenarios.

    case IDM_EDIT_SEARCHONINTERNET:
    {
[...]
      if (nppGui._searchEngineChoice == nppGui.se_custom)
      {
[...]
        {
          url = nppGui._searchEngineCustom.c_str();
        }
      }
[...]
      Command cmd(url.c_str());
      cmd.run(_pPublicInterface->getHSelf());