Render a mobile-friendly piano

For now since I'm the only customer and I'm primarily making this for myself,
I'm styling the app specifically for my Google Pixel 4. If I find this app
useful, I will consider supporting other devices.

I'm using the Icons that I bought when I purchased the "Refactoring UI" book.

Other news:
- I bought the domain learnpianochords.app!

What's left:
- Style the "fine tune" tab of the preferences view
- Better support non-mobile devices like the browser and tablet devices
- Deploy the application to learnpianochords.app
- Redesign the "key" tab of the preferences view to sort the keys according to
  the circle of fifths
- Dogfood
- Simplify until I cannot simplify anymore

website/sandbox/chord-drill-sergeant/elm.json

@@ -10,6 +10,7 @@
             "elm/core": "1.0.5",
             "elm/html": "1.0.0",
             "elm/random": "1.0.0",
+            "elm/svg": "1.0.1",
             "elm/time": "1.0.0",
             "elm-community/list-extra": "8.2.3",
             "elm-community/maybe-extra": "5.2.0",