Be able to add notes by clicking on a piano

[jocelyn-stericker]

From https://news.ycombinator.com/item?id=17959107:

I sometimes try to use Denemo but the UI is a bit complicated so that writing LilyPond yourself maybe is easier? But I like that Hacklily hat some other input methods as tools. I would like to click on a virtual piano. http://www.denemo.org/