Make select config options available as command line options

[mountaindude]

Some config settings could be useful to have as command line options.

For example, when investigating why Butler isn't working as it should you may want to enable debug logging.
It's then easier to add a --loglevel debug when starting Butler than to edit the config YAML file.

It would also be useful to have a command line option via which it's possiblöe to specify which YAML config file to read settings from.

Command line options should override the corresponding setting in the YAML config file.

The settings that should be available as command line options are (to begin with)

-c, --configfile
-l, --loglevel