message: Remap <space> key action to <Ctrl+space>
diff: [backButton constrainWidth:@"40" height:@"40"];
  _backButton = backButton;
  - UIKeyCommand *command = [UIKeyCommand keyCommandWithInput:@" " modifierFlags:0 action:@selector(toggleNav)];
  + UIKeyCommand *command = [UIKeyCommand keyCommandWithInput:@" " modifierFlags:UIKeyModifierControl action:@selector(toggleNav)];
  [self addKeyCommand: command];
  }
  