Added GuiLearnSong

- Extracted most of GuiOcarina into GuiMusicBase
- Added GuiLearnSong, for learning songs
- Changed SongNote[] in ZeldaSong to an unmodifiable List
- Player must be able to see the sky in order for the last horse ridden
to teleport when playing Epona's Song
- Renamed AddSongPacket to LearnSongPacket
- Renamed addNewSong to learnSong
Renamed AddSongPacket