Add docstrings to some functions that lacked a docstring

[ArticPiplup]

Issue: Improve Documentation #107

Add docstrings to some functions that lacked a docstring. Included docstring to the following functions

Banker.py > def change_balance(id: int, delta: int) -> None:
Casino.py > def get_submodules() -> str:
GameManager.py > def remove_game(game_id: int) -> None:
GameManager.py > def game_is_full(game_id: int) -> bool:
GameManager.py > def game_exists(game_name: str) -> bool:
GameManager.py > def player_in_game(game_name: str, player_name: str) -> bool:
Modules.py > def calculator(active_terminal: Terminal) -> str:
Modules.py > def list_properties() -> str:
Modules.py > def ttt_handler(server: Socket, active_terminal: Terminal, player_id: int) -> None:

Also Removed the command section on the README.md as told to do so within the issue Improve Documentation #107