Fixing various final bugs and removing unnecessary code

* Removing main.js and plugins.js from index since they don't seem to be needed
* Clearing listener on Create Song button after creating a song (new listener gets created when clicking on Create Song button)
* Setting loadSong to only call updateInstrument when it's not a new song (since new songs set the default)
* Removing clearLoginDiv as it's no longer necessary
* Changing GetSongData from on to once because initializing Firebase channels would remove local song data
* CreateUser is no longer storing login data before doing all checking - doesn't store globally until all checks are done
* printSongList now differentiates songname IDs between user and public lists as well as handling IDs for duplicate names when spaces are involved (since removing spaces can make two names which weren't the same become identical)