bug 932108 - Tabzilla formatting issues

Repositioned the `Search` placeholder by adjusting the line-height. It was affected by css from the body.
Replace mixins.less & variables.less w/lib.less. Bug 1057419.

- Delete mixins.less & variables.less.
[fix bug 1060614] mozilla wordmark on homepage does not work in IE 6 & 7
[fix bug 1049042] Update Firefox OS FAQ page
[no bug] Add <main> element to CSS reset
[fix bug 1066661] Firefox /new page loads template-resp.less twice
Improve mozilla-accordion.js. Bug 1055830.

- Add collapse/expand callbacks.
- Add ability to programmatically create/destroy accordions.
- Add mozilla-accordion.js tests.
- Add standard GA callback JS for existing accordion pages.
- Standardize mozilla-pager.js create param to jQuery obj.
- Update accordion & pager docs.
Merge pull request #2271 from jpetto/bug-1055830-mozilla-accordion-improvements

Improve mozilla-accordion.js. Bug 1055830.
Merge pull request #2274 from alexgibson/add-main-element-css-reset

[no bug] Add <main> element to CSS reset
Bug 1065744 - update steering committee date
Merge pull request #2275 from alexgibson/bug-1066661-firefox-loads-css-twice

[fix bug 1066661] Firefox /new page loads template-resp.less twice
Merge pull request #2276 from craigcook/bug-1065744-update-steering-committee

Bug 1065744 - update steering committee date
Bug 1065744 - add Andreas Gal to steering committee
Merge pull request #2277 from craigcook/bug-1065744-update-steering-committee

Bug 1065744 - add Andreas Gal to steering committee
Merge pull request #2249 from rubenvereecken/new-issue-932108

bug 932108 - Tabzilla formatting issues
[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
Merge pull request #2257 from alexgibson/1060614-mozilla-wordmark-ie7

[fix bug 1060614] mozilla wordmark on homepage does not work in IE 6 & 7
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.