First draft of Singing
Merge remote-tracking branch 'origin/dev' into singing-creatures
Refactoring: "Singing" interface is now named "Singer"
Refactoring
Removed useless imports
Added toString
Minor change for Coords2D: toString()
Added SoundVehicle and relative interactions with Singer animals
Created Note class
Singer animals can sing a song (starting a new thread)
Bugfix: provisional bugfix for concurrency problem
Removed useless "todo"
Added SongListener
Added source of sound to SongListener
Sound listeners would follow sounds
Override equals() for Coords2D
Fixed soundwaves drawing
Sound waves for singer animals
Fixed sound waves interception