Add keyboard shortcuts to toggle between list and task list formats

[nikifutaki]

I've added a shortcut key that allows you to toggle multiple lines between List and Task List formats, just like the Check/Uncheck function.

[yzhang-gh]

Thanks for the nice work!

However, I tend to be a bit conservative about new keybindings as there might be conflicts with some other keybindings for other users (e.g. #832, #878, #995, #1007). So I would prefer to introduce keybinding only if it is requested by many users.

Let's leave this open for now and collect more feedback from the community.