Completed Song/SongRepo classes.

-For Song class:
1. class initializes with 5 properties
-For SongRepo class:
1. creates songs table in songify-db
2. drops songs table for testing purposes only.
3. takes in params and adds it to the songs table
4. finds_by id
5. finds all instances in songs table
6. builds results into an intance of the Song class.
-Made all required relatives with correct pathing.
-Added a getter and setter method for the Songify.song_repo in the Songify module.
-Passed all tests in song_spec and song_repo_spec.