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

- Delete mixins.less & variables.less.
[fix bug 1043479] Update 'Nightly User' badge link on nightly firstrun page
[fix bug 1067863] Next/Prev button flicker in onboarding tour
Bug 1064318, Bug 1067333, Bug 1066151, Add new partners for France on devices page
Merge pull request #2255 from jpetto/bug-1057419-consolidate-less-include-files

Replace mixins.less & variables.less w/lib.less. Bug 1057419.
Merge pull request #2281 from alexgibson/bug-1043479-nightly-user-badge-link

[fix bug 1043479] Update 'Nightly User' badge link on nightly firstrun page
Merge pull request #2280 from alexgibson/ui-tour-disable-button-flicker

[fix bug 1067863] Next/Prev button flicker in onboarding tour
Add FxOS GoFox F15 purchase link. Bug 1065651.

- Also add O2 to list of operators for Alcaltel One Touch Fire
  E. Bug 1068819.
Merge pull request #2288 from jpetto/bug-1065651-grameenphone-purchase-url

Add FxOS GoFox F15 purchase link. Bug 1065651.
Merge pull request #2285 from TheoChevalier/update-french-partners

Bug 1064318, Bug 1067333, Bug 1066151, Add new partners for France on de...