Default configuration file - 1.1.6

Adding @WintersMichael new feature.

This will take a default configuration file from ~/.config/mail2go/config.json without using the --config argument.

This will make it easier for automation or repeat use, this won't affect users using other methods.

Note: CLI arguments will override configuration files (from the --config argument or the default location at ~/.config/mail2go/config.json).