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.
I've done this and all the other css cleanup described below. There are 2 `ul.topnav`'s which have been untouched, since they were not explicitly mentioned. They are:
```
ul.topnav li:hover ul.subnav
ul.topnav li ul.subnav li
```
I am going to push the latest changes, so everything so far can be checked and/or evaluated on sandbox.