Add backend classdiagrams

diagrams/backend/controllers.png

diagrams/backend/gameHandler.png

diagrams/backend/index.png

diagrams/backend/interfaces.png

diagrams/backend/middleware.png

diagrams/backend/models.png

diagrams/backend/routes.png

diagrams/backend/schemas.png

diagrams/backend/src.png

diagrams/frontend/DiagramFindGameController.png

diagrams/frontend/DiagramGameController.png

diagrams/frontend/DiagramLeaderboardController.png

diagrams/frontend/DiagramLoginController.png

diagrams/frontend/DiagramMainMenuController.png

diagrams/frontend/DiagramTankWars.png

diagrams/frontend/DiagramTerrainController.png