songs array now clears on every new query

- array is dynamically created on every query inside the appendResults method
Playlist.add callback now return song hashes
add-song-button class now has click event listener

- getSong now functional with correct array call
song_url adds consumer key
calls to song_url replaced with  song.stream_url

- song is now an object literal from SC, requring secondary call
move adding to songs object into new function

- songHash also includes new variable MLDStream that adds streamable URL
song.stream_url changes to song.MLDStream

MLDstream attribute stores stream_url and consumer key