Fix key binding of already grabbed action

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Preserve Shift in XKeyGrabber

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Refactor MediaKeys to use XKeyGrabber

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>