track song duration in store

[RaasAhsan]

we can use youtube-dl to print the song duration, which can then be persisted in a column in the table for songs. we can do some interesting things with duration:

• sort songs by duration
• show how long a song is
• show how much time is left in a song: timeStartedPlaying + songDuration - timeNow

[RaasAhsan]

to migrate to avoid data loss, we can apply our sqlite migration to add the column, then execute a script that fills in empty durations.