Rework config and save to playlist arg

[Badgie]

Decided to rework the config files as well, so this PR will be a bit more comprehensive than expected.

• Rework config to use one file, rather than 5 - see below
  • This is managed through conf.py.
• Make config modifying argument names more uniform
  • Most (sans blacklist) will follow a --[remove|save]-TYPE scheme.
• Make functions relevant to the above arguments more uniform
• Added function that converts old config to new
• Allow adding and removing currently playing track to specific playlist
• Allow saving and removing playlists in config
• Update README
• Use case test on everything
  • no-arg with and without n
  • -a with and without seed size
  • -t with and without seed size
  • -ac
  • -tc
  • -gc
  • -gcs
  • -c with different type inputs
  • -s
  • -sr
  • --add-to with saved list and uri
  • --remove-from with saved list and uri
  • --save/remove-playlist
  • --save/remove-device
  • --save/remove/load-preset
  • -l with any
  • --tune with any
  • --play
  • -b, -br, -bc
  • all --print

Config structure:

$ cat ~/.config/spotirec/spotirec.conf
[spotirecoauth]
access_token = str
token_type = str
expires_in = int
refresh_token = str
scope = str
expires_at = int

[presets]
preset-id = dict

[blacklist]
tracks =dict
artists = dict

[devices]
device-id = dict

[playlists]
playlist-id = dict

Stuff to fix when merging the remaining PRs:

• Implement graceful keyboard interrupt handling for new input prompts
• Maybe set default playlist as a saved playlist

[falkecarlsen]

Pedantic stuff, otherwise very nice!