Style bubbles with gray outline, remove mouseover code

 - d3.select(this) was selecting "g" elements, not circles.
Move #detail for loop (populating ul with data points) into mouseover handler.

This allows a user to see more about a bubble at mouseover, rather than on click.
In d3.layout.pack, change sort function to return bubbles arranged by d.score (in reverse order, with higher scores appearing closer to the center)
Replace for-loop over data details with text insertion into pre-created list elements in #detail div.

 - Add li's with ids in app.js in success callback
 - Insert text from d3 on mouseover
 - Include '@' symbol and labels for data
 - Remove bullet style from list