Add seed data for purchased songs

[poppabear8883]

Need to add dummy data to the song_user pivot table. This data refers to the songs a user account has purchased.

This task should included:

• [x] Completed migration for the song_user pivot table
• [ ] Completed relationships on both models (a user has many purchased songs, songs have many users that purchased it)
• [ ] Completed seeder for the model

[cbj4074]

This will work for now, but longer-term, there is additional complexity here.

When a customer adds a song to his cart and purchases it during checkout, the Order is persisted to the database. The order details contain information about which songs the customer purchased and at what price. Capturing this information is necessary for sending the Order Confirmation email, displaying the customer's Order History, and determining how much the Artist is owed.

In other words, the relationship between a customer (User) and a Song exists through a series of other relationships that are more complex than they first appear.

We can flesh this out further once we have the Digital Catalog completely ironed-out.

[poppabear8883]

• The migration task is complete on this issue

• The Song Model has the users relationship, however the User Model still needs the songs relationship.

• No seeded data for this implementation as of right now