AudioBrowserFragment: focus related improvement

Signed-off-by: Geoffrey Métais <geoffrey.metais@gmail.com>
AudioPlayer Header: focus related improvement for R.id.header_play_pause

Signed-off-by: Geoffrey Métais <geoffrey.metais@gmail.com>
focus related resource improvements

Signed-off-by: Geoffrey Métais <geoffrey.metais@gmail.com>