Aesthetic changes to UI, pass 2

* Crisp edges for y-axis grid
* 'Statistics' orange color updated with orange from style guide
* Added top margin to .bars
* Removed inset shadow
* Removed monotone interpolation
* Thicker paths
* Cleaner grids, removed axes, fewer x-axis labels, x-axis labels no
longer rotated
* 'Update' button label changed to 'Apply'
* Formatted numbers in tooltips (e.g. 1000 -> 1,000)
* Hovering on a series name in the legend dims the other series rather
than thickening the selected path
* Removed 'Total' from chart names since it seemed unnecessary
* Replaced logo with one resized using "bicubic sharper" since the
in-browser resampling was making it look fuzzy in Firefox (it was fine
in Chrome)