sound applet: add deadbeef support (closes #1351)

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
sound applet: add support for smplayer

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
Merge pull request #2001 from nkoep/deadbeef_support

[2.0] sound applet: add deadbeef support (closes #1351)