To Master - User can get all playlist. Updated Endpoint

[MackHalliday]

Issue Number: #32

Description of Behavior

Update endpoint GET api/v1/playlists to include information about playlist songCount and avgSongRating. Also includes playlist's favorites, with information on each favorite.

Pull request checklist

Please check if your PR fulfills the following requirements:

• [x] Tests are written
• [x] Test coverage acceptable
• [x] Sad paths accounted for
• [x] Tested in browser

Merge to

• [ ] Development branch
• [ ] Staging branch
• [x] Master

Additional Comments