Improve launch speed of "Volumes" in Settings/Sound

There is a delay after pressing volume menu item
there is a delay until the Volume popup is shown.

The reason for this is that the initialization of
the different seekbars is slow and run in the main
thread. More specifically the call to get the
ringtone from the RingtoneManager is causing this
delay.

Moving the call to the ringtone manager to the
handler thread used to play ringtones to make
the launch of the volume dialog a bit snappier.

提升 设置/声音 中"音量"的启动速度

当按下上述"音量"按钮时有较严重的延时, 音量调节面板
不能迅速的弹出.

导致这个问题的原因是初始化这几个分类音量滑动条
的速度很慢并且占用主线程. 具体而言, 是获取
RingtoneManager的铃声导致的这个延时.

将mRingtone = RingtoneManager的调用改为
mHandler, 也就是播放铃声的线程. 从而让音量调节
面板的启动更流畅.