Add watch whole concert functionality

- Added youtube_it gem
- Created new service class - CreatePlaylist - that handles creating the playlist and adding videos (may want to change the name)
- When concert is created, I create the playlist, saving the playlist ID as an attribute on concert
- Songs are added to the playlist as users click add song on the results show page
- When you view the concert page now, I embed the concert playlist ID in the YouTube JS player code to pull in the video playlist of the specific concert