Setup & Configure A Database to Store Spotify Access Tokens

[BrandonErik-FS]

• [x] Create a UserToken Mongoose model to store user tokens in MongoDB.
• [x] Add a function to save a UserToken to the database.
• [x] Add a function to update a UserToken in the database.
• [x] Add a function to find a UserToken in the database.

[BrandonErik-FS]

I created a UserToken Mongoose model to store user JSON web tokens in the MongoDB database. I also added find, create and update functions within the spotifyController and validateToken files to save and update any token as needed in the database.