adds check for remove from playlist flag

[jasonhamilton]

If the remove from playlist setting arg is set to false the software still tries to remove from playlist. It looks like when the previous method was deprecated a flag check was forgotten, so the software always tries to remove from playlist.

[jasonhamilton]

Adds functionality to make the software more extensible.

1. Adds a hook so an external program can monitor when tracks get loaded - Allows you to create a ripper object, extend from the object and implement a hook to handle tracks (save info to DB, etc) when loaded.
2. Separates the file re-namer function into two separate, de-coupled components so the renamer can be used without an active ripper/spotify session. Imagine if you save a track and all its attributes but later want to rename it using the same format_string.
3. Allows the progress object to be selected at runtime. This allows you to import and extend from the progress object then load it into the ripper module when it is instantiated so you get all dat object inheritance goodness. Oohh wee!

[gianpaj]

Please accept this pull request! @SolidHal

otherwise, playlists are emptied by default!

[SolidEva]

Closing this pull request, reference my comment on: #23