Refresh the UI with a Treeherder color scheme (#111)

This addresses issue #111, updating the legacy Netscape color theme to one which will match Treeherder going forward, [as mentioned by Dave](https://github.com/mozilla/mozmill-dashboard/issues/111#issuecomment-45846780).

The total changes, including some minor UI tweaks to make it look cleaner, are:

* removal of unused menu png's - replaced by solid color matching Treeherder
* 1px black divider lines added to the menu block matching Treeherder
* white main-menu hover text color for more perceptible hover
* solid color panel removal from the Report Information table
* bold text removal from Report Information table
* 5px table padding removal from Results tables
* bold removal from row1 Results tables
* half-luminance 'unselected' sort-icon for row1 Results tables

I had to add a discrete css selector for the Report Information table to re-add the 5px padding removed during the overall table padding removal. Otherwise that table looked too compressed against its boundary.

Adding @whimboo for visibility.
@whimboo I've done the alternating background colors, using `#f7f7f7`. It looks nice, however the alternating is uniform only in Reports, and Report (Filter: All). When in Report (Filter: Passed, Skipped, Failed) the reshuffle will give random groupings of color. It's not horrible, but here's a screen grab:

![wipui_alternaterowcolorsski](https://cloud.githubusercontent.com/assets/3660661/3361627/8bb1e984-fb00-11e3-9f62-0619c3fbe183.jpg)