Match job pinning keyboard shortcut to TBPL (1033268)

This work fixes Bugzilla bug [1033268](https://bugzilla.mozilla.org/show_bug.cgi?id=1033268).

The key event `spacebar`, now pins the selected job to the pin board. If no job is selected the method is bypassed. I've tested a variety of jobs, with 

* new pin (jobs page down suppressed)
* single, multiple pins (as above)
* pinning with a collapsed pin board (job counter increments, page down suppressed)
* re-pinning to a cleared pin board
* spacebar event with no selected jobs (page down event)
* spacebar event with closed job details panel (page down event)

and it appears to behave correctly on both Firefox and Chrome. A big thanks to @camd for helping me worth through the mystery of Chrome working and internally setting the event, where Firefox was not.

Tested on Windows:
FF Release **30.0**
Chrome Latest Release **35.0.1916.153 m**