Adds links to the playlists to show the details of the playlist.
Remove unnecessary models.
Adds bundle model to joins startups and playlists.
Fixes rebase conflicts.
Adds route support to add a bundle and to interact with bundles.
Adds destroy route support for bundles.
Adds Bundles controller to add create and destroy actions.
Removes unnecessary routes definition
Adds support for adding a startup to a playlist.
Adds validation to the playlist.

Adds validation so that each playlist can add a startup only once.
Adds eager loading on the playlist.
Refactors relatioship declarations between models.