Add plugin: Additional keybind on song selection

[mirusu400]

Sorry for much PR's;

I've add more shortcuts like Search(Ctrl+F)

Here are lists that I added.

* Ctrl+P => Open Plugin Setting
* Ctrl+S => Open Settings
* Ctrl+R => Select Random Song
* Ctrl+C => Open "Custom Song List"
* Ctrl+M => Mute Song (You can also mute song by pressing Q key)