refactor: added singleton class to hold information for controllers

What are the key features of this change

Added a BattleSimulationSingleton class which holds the information of the original and current armies, current battle, scores, filepaths and more. This removes coupling between the BattleController and EditArmyController. Also moved tests into other packages for structure.

closes: None

Size of change: medium

Checklist

• Javadoc is added to methods and classes
• Tests are added to feature
• Build tool test passed