- Electron version: 1.3.6
- Operating system: Windows 7 x64
- Other: Microsoft Office 2013 (will make more sense in a bit)

`shell.openItem()` is a blocking call, it would be nice if it's async or has an async version to handle synchronous external application behavior.

Reproduce: 
Open a password-protected Microsoft Excel file, `shell.openItem()` will be blocking until the Password window is submitted or dismissed. Consequently Microsoft Word does not have this issue.

Related to #2761.

shell/common/api/atom_api_shell.cc
const base::FilePath& path) {
  using base::win::ShortcutProperties;
  gin::Dictionary options = gin::Dictionary::CreateEmpty(thrower.isolate());
  base::win::ScopedCOMInitializer com_initializer;
  base::win::ShortcutProperties properties;
  if (!base::win::ResolveShortcutProperties(
          path, ShortcutProperties::PROPERTIES_ALL, &properties)) {
    thrower.ThrowError("Failed to read shortcut link");
    return v8::Null(thrower.isolate());
  }
  options.Set("target", properties.target);
  options.Set("cwd", properties.working_dir);
  options.Set("args", properties.arguments);
  options.Set("description", properties.description);
  options.Set("icon", properties.icon);
  options.Set("iconIndex", properties.icon_index);
  options.Set("appUserModelId", properties.app_id);
  return gin::ConvertToV8(thrower.isolate(), options);
}
#endif
void Initialize(v8::Local<v8::Object> exports,