Improve use of scenes in /firefox/new.

See bug 919788.

This makes a few changes:

 * if you arrive on the page directly from #download-fx the animation is suppressed.
 * dowload is initiated in an iframe so current page CSS images don't get cancelled before loading.
 * scene2 is suppressed on Android
 * fixed bug in IE < 9 going directly to #download-fx
 * improve inline commenting
 * use LESS-CSS mixin for transitions in CSS.
Open popul before sending GA tracking.

Seems to prevent popup blocker in some cases.
devices.csv sept update
Bug 892470: enable plugincheck redirect for ca, he
Merge pull request #1277 from flodolo/plugincheck_cahe

Bug 892470: enable plugincheck redirect for ca, he
Merge pull request #1276 from AaronMT/sept-devices-update

devices.csv sept update
Redirects for /projects/devpreview for Bug 858315
Merge pull request #1275 from gauthierm/improve-use-of-scenes-on-new

Improve use of scenes in /firefox/new.
Redirect locale-specific proect pages (Bug 885856)
Merge pull request #1280 from sgarrity/bug-885856-projects-index

Redirect locale-specific proect pages (Bug 885856)
[bug 919581] Update copy on mission and about pages
Merge pull request #1279 from alexgibson/bug-919581-update-copy-on-mission-and-about-pages

[bug 919581] Update copy on mission and about pages
Merge pull request #1278 from sgarrity/bug-858315-devpreview

Redirects for /projects/devpreview for Bug 858315
Bug 916151 - home page redesign

With contributions from @pmclanahan, @alexgibson, and @pascalchevrel
Merge pull request #1269 from mozilla/bug-904696-homepage-redesign

Bug 916151 - home page redesign
Cache-bust images on Firefox OS Style Guide Pages
Bug 922704
Bug 919042 - /newsletter/existing l10n

* Wrap "Submit" button on updated page for translation.
* Add comment to "existing" page template reminding that the newsletter
  description is already translated in the view code, and doesn't need
  to be wrapped in the template.
Bug 923025 - Enclose strings in l10n calls for /mission
Merge pull request #1287 from pascalchevrel/bug-923025_l10nify_mission_page

Bug 923025 - Enclose strings in l10n calls for /mission
Merge pull request #1283 from sgarrity/bug-922704-styleguide-cache

Cache-bust images on Firefox OS Style Guide Pages