DeepCave should probably raise a warning, if an optional dependency is missing

[LukasFehring]

Upon loading a ray run in the web interface the following warning is raised, if ray is not installed

RunHandler (WARNING): Run /home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1 could not be loaded. Please check the logs.
RunHandler (WARNING): AMLTK: [Errno 2] No such file or directory: '/home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1/configspace.json'.
RunHandler (WARNING): BOHB: [Errno 2] No such file or directory: '/home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1/configspace.json'.
RunHandler (WARNING): DeepCAVE: Could not load trials because trials were not found..
RunHandler (WARNING): Optuna: The Optuna package is required to load Optuna runs. Please install it via `pip install deepcave[optuna]`.
RunHandler (WARNING): RayTune: No module named 'ray'.
RunHandler (WARNING): SMAC3v1: [Errno 2] No such file or directory: '/home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1/configspace.json'.
RunHandler (WARNING): SMAC3v2: [Errno 2] No such file or directory: '/home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1/configspace.json'.
RunHandler (WARNING): DataFrame: [Errno 2] No such file or directory: '/home/lukas/Desktop/DeepCAVE/logs/RayTune/run_1/trials.csv'.

It is easy to miss that the ray dependency is missing. It would be cool if there was a more obvious popup

[mwever]

Solved with #231