Bug 1103425 - Add a bit more polish to the pinboard

This work fixes Bugzilla bug [1103425](https://bugzilla.mozilla.org/show_bug.cgi?id=1103425).

This adds some more layout improvements to the pinboard, specifically to:

* address past concerns the job panel/pinboard was too heavy/dark/high-contrast
* 'tie' the pinboard to the job panel, but present it as separate functionality
* maximize available space for pinned jobs, bugs
* retire icons which don't do anything
* eliminate unnecessary labels, headers where possible
* imply functionality and context

In the code, among the changes we:

* add a new `hasRelatedBugs()` function to support suppression of the related bugs message
* remove some now-unnecessary hover styling for the pinboard button
* remove the extra close icon in the pinboard (top right corner)
* shrink the resizer as much as we can get away with
* continue with the min/max-height containers but make them 80/120 instead of 60/120
* tweak wording of the pinboard message per KWierso's request

Here is a before and after:

![pinboardcurrent](https://cloud.githubusercontent.com/assets/3660661/5204333/89d069ac-755c-11e4-8a3e-93e1174fb3ba.jpg)

![pinboardproposed](https://cloud.githubusercontent.com/assets/3660661/5204334/8cde22a6-755c-11e4-84e5-77cd4ab0655a.jpg)

The actual screen space consumed by the pinboard is identical, and all optimizations happen within that space.

I've tested it pretty extensively on Windows and @camd had a go yesterday on OSX with an earlier wip branch. We'd probably want to let everyone try it out on dev for awhile. A note, for clean related bug additions in the console, this PR requires PR https://github.com/mozilla/treeherder-ui/pull/278 to be merged first.

Tested on Windows:
FF Release **33.1.1**
Chrome Latest Release **39.0.2171.65 m**

Adding @camd for review and @wlach for an extra set of eyes on the change.