Add (de)serialization to all settings classes

[dokempf]

All settings classes should be trivially serializable to JSON/YAML etc. For that purpose, it would make sense to extend the model base class with these capabilities. I would propose to add the following:

class SomeSettings:
	def to_dict(self) -> dict:
		# Return a Python dictionary with the class

	@classmethod
	def from_dict(cls, data: dict):
		# Construct from a dictionary

	def to_yaml(self, filename: Path):
		# Write a YAML file, using to_dict

	@classmethod
	def from_yaml(cls, filename: Path):
		# Create from YAML file, using from_dict

	def to_json(self, filename: Path):
		# Write a JSON file, using to_dict

	@classmethod
	def from_json(cls, filename: Path):
		# Create from JSON file, using from_dict

I do not think the particular choice of YAML or JSON is relevant here, might as well allow both. The import bit is that the writing and parsing is implemented in exactly one place to minimize the overhead of having both.