Support Arrow keys for going back and forward 15 Seconds

[bigfatbird]

Hi, not sure if I'm right here?! Been listening to some of the shows on Podlovers, where I think you are dogfooding the software.

Expected behaviour:

1. When listening to a Podcast on a site it would be nice to have the ability to move back and forward the 15 Seconds when pressing the left and right key.
2. You can get an inspiration of this behaviour while watching a youtube video.
   When a user watches a video, he can skip 10 second ahead when pressing the right arrow key on the keyboard for example.

Behaviour right now:

1. Nothing happens on the site when pressing the left and right keys

Example:

1. You can reproduce the example on the site of the Podlovers, while listening to a show.

[alexander-heimbuch]

That should already work for the Web Player. I will transfer this issue to the podlovers repo.