Add State of Mozilla 2012 page. Bug 928120.

- Update video helper to accept 'preload' & 'id' attributes.

- Add image replacement class to sandstone/lib.less.

- Add default title style to mozilla-modal.js.
- Update video links for non-JS/screen reader users.

- Minor copy updates.
- Add focus/hover styles to video links.

- Small copy/text changes.
Merge branch 'bug-928120-state-of-mozilla-2012' into demo-3-branch