Feature: Now Playing Percentage

[jonstuebe]

On a lot of players like audible and the like, they show in the now playing view a progress percentage. This is super helpful for filling out things like goodreads and fable. I know there was an older issue to add your reading progress percentage but that's a little buried and you have to exit your now playing view to see it.

I'm going to attach a PR to this issue, let me know what you think.