Update /firefox/whatsnew with FxOS messaging. Bug 890114.

- Specified locales get FxOS messaging.

- Old messaging retained for legacy/other use.

- Update l10n_utils render function to handle list of
  templates.
Merge pull request #1322 from mozilla/bug-890114-promote-fxos-whatsnew

Update /firefox/whatsnew with FxOS messaging. Bug 890114.