Bug 1059279 - Improve resultset menu bar clarity and cancel access

This fixes Bugzilla bug [1059279](https://bugzilla.mozilla.org/show_bug.cgi?id=1059279).

This improves access to the frequently used "cancel all" jobs, by breaking it out into a separate button. And at the same time retiring the existing icon for the mcMerge menu, so it is consistent with similar drop downs in the upper navbar - which also only have a down-arrow/chevron.

Net, it adds roughly 1/2 a button width to the entire bar, since we remove part of the width of one (the mcMerge menu icon), and add one for cancel all jobs. A by product we end up with three nice and fairly consistently sized buttons.

Here is a before and after:

![resultsetbuttonscurrent](https://cloud.githubusercontent.com/assets/3660661/4431574/a174e894-466d-11e4-9e70-21ae8eb34f01.jpg)
![resultsetbuttonsproposed](https://cloud.githubusercontent.com/assets/3660661/4431575/a396a3ec-466d-11e4-8e9e-b1f52566a65e.jpg)

We also have a suitable tooltip:

![resultsetcanceltooltip](https://cloud.githubusercontent.com/assets/3660661/4431577/adbdf15e-466d-11e4-8f03-4e3067eac10a.jpg)

I took the opportunity to decrease the contrast of all these glyph icons in the bootstrap, increasing the glyph color grey to `#666` so they compete less with the jobs. It differentiates on hover and looks nice on Windows but let me know if it seems too light on OSX. I understand from @wlach we can update the bootstrap and not risk it getting stepped on by bootstrap version updates.

The default proportions for glyph `minus-sign` were a bit powerful, so I reduced its size by 15% so it better matches its neighbors.

Tested on Windows:
FF Release **32.0.3**
Chrome Latest Release **37.0.2062.124 m**

Adding @camd, @wlach and @edmorley for feedback and review.