Replace mixins.less & variables.less w/lib.less. Bug 1057419.

- Delete mixins.less & variables.less.
[fix bug 1049042] Update Firefox OS FAQ page
[fix bug 1067281] Remove duplicate CSS files from bedrock pages

- /mission/
- /about/powered-by/
- /firefox/channel/
- /firefox/os/devices/
- /about/manifesto/
- /plugincheck/
- /privacy/ base template
- tabzilla.less imported lib.less twice
Fix bug 1066629: Add contribute.json
Merge pull request #2268 from pmclanahan/add-contribute-json

Fix bug 1066629: Add contribute.json
Add GoFox F15 phone to FxOS devices page. Bug 1065651.
Merge pull request #2273 from alexgibson/bug-1049042-update-firefox-os-faq

[fix bug 1049042] Update Firefox OS FAQ page
Merge pull request #2278 from alexgibson/bug-1067281-remove-duplicate-css-files-templates

[fix bug 1067281] Remove duplicate CSS files from bedrock pages
Merge pull request #50 from mozilla/bug-1065651-fxos-gofoxf15-device

Add GoFox F15 phone to FxOS devices page. Bug 1065651.
Revert "Add GoFox F15 phone to FxOS devices page. Bug 1065651."

We will hold this until further notice.

This reverts commit 4a79bdd7fd3f03c7beef98beb717c7978a6f3969.
[fix bug 1043479] Update 'Nightly User' badge link on nightly firstrun page
[fix bug 1067691] Stop redirecting Firefox Sync pages to Mozilla Taiwan website
[fix bug 1067863] Next/Prev button flicker in onboarding tour
Fix bug 1068105: page helper to skip l10n redirect based on full request path.
Merge pull request #2284 from pmclanahan/fix-page-url-util-l10n-exempt

Fix bug 1068105: page helper to skip l10n redirect based on full request path.
Revert "Revert "Add GoFox F15 phone to FxOS devices page. Bug 1065651.""

This reverts commit 8ff201e3060ca0b7707076b9475dcbd5d593d2af.

Reverts all the way down.
Bug 1064318, Bug 1067333, Bug 1066151, Add new partners for France on devices page
Fix Bug 1068413 - Change canonical, alternate, and Open Graph URLs from HTTP to HTTPS
Merge pull request #2286 from kyoshino/bug-1068413-canonical-https

Fix Bug 1068413 - Change canonical, alternate, and Open Graph URLs from HTTP to HTTPS
Merge pull request #2255 from jpetto/bug-1057419-consolidate-less-include-files

Replace mixins.less & variables.less w/lib.less. Bug 1057419.