Add FxOS anniversary page. Bug 1032279.

- Add GA to FxOS anniversary page. Bug 1046844.

- Add 'findPageById' to mozilla-pager.js.
- Add options param to mozilla-pager.js to allow for
  onCreate callback.
- Document 'currentPage' property of mozilla-pager.js.
- Move custom easing methods in mozilla-pager.js out of
  document.ready.
- Standardized indentation on firstrun.js (no code changes).
It's really just because the image for the logos is a sprite, so both the fox and the wordmark need fixed dimensions. If the fox were the background on `#fxos-logo-wrapper`, the wordmark would bleed out to the right.

Basically a choice between fewer image requests and less markup. I chose the former. :smile: