ArrayLists changed to processing.data.IntList and processing.data.StringList where applicable.

audiolistUI.java
-Removed selectedSongList instance variable and replaced with selectedIndex instance variable.
-Changed permissions of addToList() method from protected to private.
-Removed unused isSongSelected() and removeFromList() methods.
-Replaced addToSelectedSongs() method with controlEvent() callback method to handle both selected and deselecting songs.
-Only songs not already loaded are added to list.

PopupDialogue.java
-Removed instance variable controlp5.
Only songs not already loaded are added to list.