Makes TheLastBarcodeSymphony.java a singleton

oh god I hope I did this right
Merge remote-tracking branch 'origin/Singleton-main-class'

Conflicts:
	core/src/main/java/com/eshsrobotics/the_last_barcode_symphony/core/PauseScreen.java
	core/src/main/java/com/eshsrobotics/the_last_barcode_symphony/core/PlayScreen.java
	core/src/main/java/com/eshsrobotics/the_last_barcode_symphony/core/TheLastBarcodeSymphony.java