Play plugin: Allow specifying display title using extended m3u

When using the `play` plugin, the generated m3u file is currently a list of the file paths.

Via [Extended M3U](https://en.wikipedia.org/wiki/M3U#Extended_M3U), it could allow the user to configure a custom title for every item using a format string. Media players supporting this will profit from a more configurable playlist.

Low priority.

Start by locating the play plugin and reading how it currently generates m3u entries and exposes configuration. Define how a per-item title format should be configured, then verify that generated playlists use Extended M3U titles while preserving the existing file paths and behavior.

Written by the indexing model from the issue text.