Consolidate `App` component render subscriptions

Rather than subscribing `App` component renders to both the
`pitchClasses` and `answers` observables, merge the two and subscribe
to that instead.
Break long lines
Delete unused reference to `ReactDOM.svg`
Pass `onAnswer` to `App` component as prop
Pass `pitchClass` to `App` component as prop
Pass `markCorrect` to `App` component as prop
s/var/  ,/
Factor `App` component out into its own file
Merge branch 'refactor'