Playlist numbering only feature

[AdyStudios]

Description

Added new feature, which is a stripped down version of the playlist numbering. This only changes the index of the song, sets it to the same as in the playlist.

Motivation and Context

Added feature because it helps with created playlists on offline devices, where the m3u file is unusable (eg. Winamp).

Issues

Currently does not wok with saved songs.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project, mostly
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have read the CODE OF CONDUCT document
• I have added tests to cover my changes
• All new and existing tests passed

Excuse

I'm not a very experinced developer in this envrioment, so I was unable to do everything from the checklist, if you think this feature is good, I appriciate your help, but this was made mostly for myself.