Add scroll bar below the song/graph visualization chart

[franklee77]

The scroll bar should be connected to the sound and visualization engine so that the user can skip forward/backward.

[jo-im]

If there is an overflow of content in the placeholder div then you are able to see the scrollbar where you can go forward and backward. I tested by putting a long text and you can see a horizontal scrollbar at the bottom of the div. However, I did not put any content inside so you can't see the scrollbar. But if you would like, I can put a placeholder content inside the div so everyone can see the scrollbar!