Default "Now Playing" image is dependent on KWVA theme

[Pythagory]

Our template for the "Now Playing" shortcode has support for a default image, but it's currently hardcoded to reference an image in the active theme. Probably something from early development of the KWVA site that never got cleaned up, will want to replace this with something more sensible. Offending code starts around line 15 of views/nowplaying.php.