Add Treeherder to js/py programming language categories (1046596)

This fixes part 1 of Bugzilla bug [1046596](https://bugzilla.mozilla.org/show_bug.cgi?id=1046596).

This adds the suitable Treeherder content to both js/py categories. @jdm please check to make sure the py granularity level (ie. a sibling to items like "Release Enginnering" and "Firefox") makes sense to you. I've only updated en.ini based on the older checkins to the repo where new items were similarly added. I assume the other locales get suitably generated.

Let me know if I've missed something. I've iterated with @jeads on the wording and he's happy with it.

Tested on Windows:
FF Release **31.0**
Chrome Latest Release **36.0.1985.125 m**
No need for a second one if the strings are the same. Just get rid of of the js/py prefix and share them.