Add progress bar to the music player

[chrislo]

A little bit of feedback from one of the artists I've been adding to the site:

I haven't looked on computer yet but to me the only thing missing right now on mobile is a track progression bar! It plays smooth and all but it seems to start at the beginning with no way of skipping through the track's length

It's something I often do when first checking out albums on Bandcamp. I sometimes just want a quick glimpse so I jump in the middle and then save the actual listening for after my purchase when it's downloaded and ready for the sound system!

We'll have to have a think about how to fit this into the design, but perhaps a small horizontal div beneath the play controls. The HTML5 audio tag supports jumping to specific time points and reporting the current position so we should be able to hook this into the existing Stimulus controller.

There's other small improvements we might want to make too:

• display the track length and current position within the track when previewing the album using the player controls. That is, some kind of text indication of the current time/remaining time next to the the track title in the player
• display the first/preview track title by default, it's currently hidden until you press play.