Bug 841760 - Lazyer Settings app - CSS Part
(cherry picked from commit 2f86aad75e00ffd578f8f5245fcde81af2ef516d)
Bug 829066 - tests in settings should test one file at a time r=etienne a=tests

about_test.js only tests about.js now, removed the call to settings.js and
mocked it instead.

Also made mocks_helper call a function for each step.
(cherry picked from commit 3586a01dbae113903de7a772f14ab34ac444e55b)
(cherry picked from commit c481c39548d79dcf948eceda740efb373f2be3e8)