art to Discord RPC (Security issue)
GStreamer's GError is a struct, not a char*, with GError->message being
the actual char* message.
Since Subsonic/OpenSubsonic servers don't have a way of sending cover
art unauthenticated, sending cover art to Discord using Discord RPC
exposes an authenticated URL to Discord servers (But only Discord since
it is then proxy'd). Added a config option to disable this behavior and
only use the app icon if the user doesn't feel comfortable enough to
trust Discord (understandable tbh)
