Write some end to end tests

[bryanbraun]

I told myself I wouldn't have to do this until I shipped some bugs. Well, I shipped some bugs.

I'm probably going to use Cypress, and start it out with just a couple of high value tests for creating songs, and using controls.

Test ideas:

• [x] Confirm Page Defaults
• [x] Loading a V0 song
• [x] Loading a V1 song
• [x] Create a new song
  • Start from an existing song, confirm that all the right things go blank
• [x] Edit an song:
  • Add a title, confirm page title updates
  • Add notes, confirm url updates and share link updates.
  • Adding a note plays the sound.
  • [x] Silent notes?
• [x] Extend an existing song in various ways.
  • Add new pages, remove new pages, add notes to new pages, confirm that you can't remove those pages,
  • Add extra pages, reload the webpage, and confirm that the correct number of pages is showing
• [x] Change box types, and confirm all expected behaviors
  • Verify the updates for 15, 20 , and 30 notes.
  • If dropping pitches removes notes, warn the user.
  • If dropping pitches doesn't remove any notes, do not notify the user.
• [x] Playing a song
  • Push play and confirm that tonejs does something.
    • Confirm that pushing space has the same behavior.
    • Also confirm that any UI elements react to isPlaying appropriately.