Collection page

[chrislo]

Allow users to listen to music they have bought from a "collections" page.

Ideally this would include a player (possibly one that persists across the whole site), but in the first instance it'd be useful enough if it just showed the albums in the users collection and allowed them to access the downloads.

• If a Purchase is completed by a signed-in user, store the user_id with the Purchase
• If a Purchase is made anonymously but the customer_email matches a User#email then associate the purchase with that User
• If a new User signs up and there are Purchase records with that (verified) email, associatie the Purchase with the new User
• Migrate existing Purchase to add user_id where the customer_email matches a User#email
• Collection page with list of purchases
• Icon in navbar to link to collection page
• Allow user to download puchases from collection page
• #125
• Don't show "buy" button on album pages where user has already purchased

[chrislo]

I've spun out #125 to tackle later.