Add Tracks to Playlist

[klepp0]

This implements a full routine to sync common playlists between two sessions.

from musync.tidal.session import TidalSession
from musync.spotify.session import SpotifySession
from musync.sync_manager import SyncManager

spotify_session = SpotifySession()
tidal_session = TidalSession()
sync_manager = SyncManager(spotify_session, tidal_session)

sync_manager.sync_common_playlists()

This fixes #9.