Revise the way that configuration is handled.

[fpgmaas]

Priority should be as follows:

• default
• pyproject.toml
• cli arguments

The way this is currently handled with the creation of a cli_arguments dictionary in cli.py is not very nice, there is room for improvement there.

[fpgmaas]

This is currently blocking #10. bool and List[str] arguments are both added as values to the same dict with cli arguments, so from that point on mypy can not distinguish between these anymore, and the Core class does not know which arguments are booleans, and which ones are List[str].

[fpgmaas]

Cleand up the config handling and moved some of the config handling out of cli.py to config.py. However, this still does not solve mypy's type checking.