Bootstrap to later Electron version.

Use updated version of `react-musical-keyboard`.

Use custom button for closing, improve app window.

Provide relative paths to project root (where package.json lives).

Still not working, but updated README nevertheless.

Use create-react-app to use first-party `react-musical-keyboard` component.

Separate styles from template, use png images for better look and feel.

Use repository name

Tested with a real MIDI keyboard.