Static variables are not reset when exiting to the main menu

[AlexReidNZ]

Describe the bug When the player gets a game over, the static variables for the game such as the enemy stat multipliers are not reset.

To Reproduce Steps to reproduce the behavior:

1. Play the game until you get a game over
2. Return to main menu
3. Play again
4. Enemies will have a very large amount of health

Expected behavior The enemy health should be at a reasonable amount when restarting the game.

Additional context This should be a simple fix, simply call the ResetVariables() method from the GameManager script when returning to the main menu.

[PBWiseman]

Getting fixed in #53