fix: parsing of booleans from config file

[KennethWussmann]

Fixes #337

Why

Boolean values in the config are expressed as strings. Wherever we work with them, we have to parse them correctly.

For example here:

self.config["DEFAULT"][constants.CONFIG_KEY_ENABLE_TRACKING] == "True"

The user has to be precise here with their config.

That also led to #337, which describes how tracking currently cannot be disabled, because we incorrectly parse the string by treating it as if it was a boolean in tracking.py.

What

I'm adding a get_bool function to the ConfigManager to solve parsing booleans from config once. It's using configparser's own mechanism to convert a string to a boolean and accepts additional values like true, yes, on, 1 case-insensitive.