Fix bug 1071278: Update home page and tabzilla promos

* Revert home to the Lightbeam promo, removing Net Neutrality and Web We Want.
* Revert tabzilla to the Firefox OS promo, removing Web We Want
Merge pull request #2306 from craigcook/bug-1071278-update-promos

Fix bug 1071278: Update home page and tabzilla promos