Profiler cleanup (readability, JS, CSS)

- Moved values of style attributes into the CSS (in the style element)
- Reduced the number of font-family definitions in the CSS by making the
rule for the monospace font more specific
- Changed the appearance of the heading within each profiler panel to
improve readability (white on panel's color rather than panel's color on
black)
- Added some padding and the hover coloration to the active menu item to
give it a more tab-like appearance and make the active menu item more
obvious
- Fixed the JavaScript to add/remove the 'current' class on the active
menu item