Library CoreData model v2
- add trackArtistName property to 'track'
This is in preparation for album artists, where [track artist] might be
different from trackArtist.
CoreData automatic migrations using inferred mapping model
- Obtain the mapping model via inferrence
- Migrate it to a temporary file ending in .migration
- Make backup of prev version
- Move temporary file to where prev version was

removeSQLFiles() helper method to remove all DB files (i.e. .sql*)
CoreData migration mapping model: add "debugPrint()" using category
- Prints all the entityMappings, propertyMappings, valueExpressions and
  so forth that are used in the mapping model
Helpful for debugging CoreData migrations!
CoreData: simple 1:1 copy custom mapping model
CoreData: simple example of a custom mapping model
- Was tested on Library v1->v2
- Starts off with the simple 1:1 copy mapping model
- Modifies track.name to be prefixed with "hi "
- Modifies track.trackArtistName to always be "hi"
- Does this with a custom migration policy class so the functions can be
  used in the NSExpression