Add definition of 'song_other'

[laker-93]

Missing entity string definition of 'song_other' in locales. Example from en.json here. other languages seem to be missing it too:

feishin/src/i18n/locales/en.json

Line 219 in 960427f

"success": "added {{message}} $t(entity.song_other) to {{numOfPlaylists}} $t(entity.playlist_other)",

[laker-93]

I think this is also broken: https://github.com/jeffvli/feishin/blob/development/src/renderer/features/playlists/components/add-to-playlist-context-modal.tsx#L199

The form attribute should be:

'form.addToPlaylist.success'

[kgarner7]

Resolved by #473! The correct field is track_other. Practically though, it would be nice to use the pluralized form with count where appropriate...