[FR] Introduce a config file

[B00tLoad]

Is your feature request related to a problem? Please describe.
Supplying configuration via the command line is a bit clunky.

Describe the solution you'd like
A config file to set all values

[B00tLoad]

When implementing please have a look at the config setup over at https://github.com/B00tLoad/SpotifyDedupe and try to make it as close to that as possible.

Musts for merging a pull request:

• use TOML for the config file
• save it at "~/.bsu/lfm2s"
• implement a default config file, and check if it has been changed before running the tool
• should self-fix on version change

Feel free to port the setup from the dedupe tool over to this, I don't have the time for it right now.