So... I meant to just add Artist functionality on this branch. Instead of actually doing that, I implemented CoreData for Songs. It works now! As a result, the app has a persistence mechanism upon which we can build.
delete Book & Author from my branch since Book was implemented on master and now this branch is behind.
Merge branch 'addArtist'
Merged addArtist branch (which added CoreData) into master (where Grace has added Book, BookViewController, etc.). Fixed a bug where deleting did not propagate to CoreData. Set up 2 Main.storyboard paths (1 for Songs, 1 for Books). Only the Songs path supports CoreData for now. TODO: So much refactoring. So much.