Bug 1059284 - Make the retrigger and cancel job buttons more clear

This work fixes Bugzilla bug [1059284](https://bugzilla.mozilla.org/show_bug.cgi?id=1059284).

This makes the retrigger and cancel job buttons a bit more clear, per the bug request.

In it we:

* replace both icons with the requested font awesomes
* slighly de-emphasize the cancel button since it is mildly 'destructive'
* make the retrigger interaction a bit more polished and communicative

Here's the before:

![cancelretriggercurrent](https://cloud.githubusercontent.com/assets/3660661/5521537/3d7f3b54-8971-11e4-95ee-e8b168518b48.jpg)

Here is the after:

![cancelalljobsproposed](https://cloud.githubusercontent.com/assets/3660661/5521474/4f6befa8-896f-11e4-898d-0de17eeb5f14.jpg)

Here is the interaction on retrigger:

![cancelalljobsproposedhover](https://cloud.githubusercontent.com/assets/3660661/5521475/66b957b8-896f-11e4-8f83-7837a86d7ef0.jpg)

We've also updated the resultset cancel all jobs to be consistent:

![cancelalljobsresultset](https://cloud.githubusercontent.com/assets/3660661/5521477/75ed883a-896f-11e4-99c4-04faf8091c4e.jpg)

We've also updated the job panel cancel tooltips to use a common wording, "Cancel this job", "Add this job", and so forth:

![cancelretriggertooltip](https://cloud.githubusercontent.com/assets/3660661/5521490/b6339984-896f-11e4-8540-bab39938849e.jpg)

Unfortunately I had to use an `!important` on the icon-green class. I'd prefer not to, but to override the inheritance of the fa classes, I didn't seem to have any easy alternative, to paint the icon when the entire element boundary has been crossed.

I created some generic `dim-` classes, in case they need to be leveraged elsewhere. They are used for the cancel button in the job panel and the resultset bar.

We needed to override the default 12px font height, and go 13 because these new icons are simply not as large as their predecessors.

Other than that, everything seems fine. I am planning other improvements to the Logviewer and Raw log icons, just a note they haven't been forgotten about. They are in a separate bug.

Tested on Windows:
FF Release **34.0**
Chrome Latest Release **39.0.2171.95 m**

Adding @camd  for review and @edmorley for visibility.