1052136 clean up mozl10n api in communications views

https://bugzilla.mozilla.org/show_bug.cgi?id=1052136
It's not a matter of taste. The fact that l10n-id is preceded with 'data-' is temporary and as we will start standardizing it soon as WebAPI, we'll move toward l10n-id and l10n-args attributes. For that reason setAttribute/getAttribute is much better than operating on datasets.

Also, getAttribute is about 300 times faster: http://jsperf.com/dataset-vs-getattribute-and-setattribute/3