Implement /firefox/android page redesign. Bug 1072953.

- Update fx nav. Bug 1073237.
- Update /firefox/mobile/ redirect. Bug 1071318.
Add SMS link for en-US users. Bug 1072953.
Add homepage Android promo. Bug 1082035.

- Fix tablet view android guy placement.
Merge pull request #2388 from mozilla/bug-1072953-fx-android-page-redesign

Implement /firefox/android page redesign. Bug 1072953.