Restructure config files

[ErikBjare]

I think that a default config section title of $appname (as in the {afk, window, spotify} watchers currently) is a bad idea.

• Change to a proper default section.

We should also handle testing settings using configparsers override functionality (override some defaults when run in testing mode), not as it's own defaults.

• Testing modes should be an override of the default, not a different default.

I also want to add comments to the config files to make them easier to edit.

• Add comments to the config files, making them friendlier to edit.

It would be nice to have some kind of argparse + configparser settings union to simplify overriding parameters using the commandline.

• (extra) Nice way to use argparse output as overrides.

[ErikBjare]

I also would like to switch to toml as the config format.