Improve failure/bug separation in failure summary panel (1059375)

This work fixes Bugzilla bug [1059375](https://bugzilla.mozilla.org/show_bug.cgi?id=1059375).

In it we:
* get rid of some unnecessary padding and utilize the space better
* reduce the size of the pin icon for the same reason
* leverage the color/style of the structured log failure line to separate the content better
* indent show/hide for readability

These changes save roughly one extra line of displayable space to the panel, and also 3-4 characters per line, before line wrap occurs. The use of the color/style of the structured log, while not totally color-blind accessible, provides readability and cues the user they are reading the same content in both parts of the platform. This seemed the most logical UI solution.

Here's a before and after:

![grokfailuresummarycurrent](https://cloud.githubusercontent.com/assets/3660661/4223002/2e2d9cc6-3918-11e4-926b-48d89ece6062.jpg)

![grokfailuresummaryproposed](https://cloud.githubusercontent.com/assets/3660661/4223005/357e5844-3918-11e4-931a-2e6edab57174.jpg)

I've added a new class for the show/hide ui to specifically target it for indentation.  We may replace show/hide with a language independent (and more compact) chevron, up one line adjacent to the last pin element to save space, as a non-blocker task.

Tested on Windows:
FF Release **32.0**
Chrome Latest Release **37.0.2062.103 m**

@edmorley has signed off in channel on the appearance in general.

Adding @wlach and @camd for review.
Sure, I can try that.