State of Mozilla improvements

* Bug 812206 - modal overlay z-index
* Bug 812338 - add link to /contribute
* Bug 811477 - alt text for video images
* Switched inline images to media function instead of the MEDIA_URL constant.
* Added hreflang to several links.
Merge branch 'master' of github.com:mozilla/bedrock
Removed menubar/menu/menuitem
Merge branch 'master' of github.com:mozilla/bedrock
Disable a failing test.

bug 815573
Cleanup docs

- Fixes some errors
- Replaces paraphrasing of the homepage with a 2-depths ToC
- Links to the coding document

bug 815144
Add documentation about how to contribute

- Git workflow
- Server setup

fix bug 815144
jingo.render is deprecated in recent versions of jingo

bug 816080
Move download button templates into their own folder

Split the helpers into different files

bug 814079
Update license to MPL 2.
Fix Python coding declaration after adding MPL2 license
Bug 816144: remove call to whatsnew.lang in root, file was moved in template pth
Turn off android animation for small screens
[Bug 815636] New: /firefox/fx looks bad with a 855px browser width
Merge branch 'master' of github.com:mozilla/bedrock
Move Google Analytics to head
final changes to ready new privacy hub landing page
Merge branch 'ossreleasefeed-bug809079-launch-new-privacy-hub-home'

Conflicts:
	apps/privacy/templates/privacy/index.html
	media/css/privacy.less
Merge branch 'master' of github.com:mozilla/bedrock
Fix bug 815731 - adding a page at /itu/
Bug 816531: fix a form string wrong on all pages for locales