Fixes bug in which user list would get overwritten after logging in and creating a new song

* Needed to change the way song names were stored in the user list on FB - instead of a string of names, each song is stored as a node, just as it is in the public list
* Changed the FB listener from once to child_added, which removed the need for the for loop
removed unnecessary userlist storage in user constructor as well as its get/set functions since printing of userlist is all done from FB now
Merge pull request #21 from artfoundry/fix-user-list-bug

Fix user list bug