Add a background music player to mage client

hi,
This feature can make mage to play music when battle panel is activated. 
The player support .wav and .mp3 files, and the music path is predefined as  'mage-client\plugins\sounds\musics\'. Player will randomly and sequentially play music files in this path
I set a check box in preference UI to enable or disable the music player.
If you like this, I'll develop more features to make the client looks bright.

thanks