Split segmentation and test execution.

Testing has shown that segmentation needs to happen early on if the bootstraping, just once per application load.

Running the test is defered to 'page:common:ready' for each page transition.
jshint fixes
Remove split property from fixtures. It's not used.
Make Omniture tag from within the AB test module

This prevents us logging data to Omniture when the test is turned off.
Neater tests
Changed AB test API from ab.init() to ab.segment()
Clarify purpose of the test
Merge branch 'ab-test-segmentation-refactor' of https://github.com/guardian/frontend into ab-test-segmentation-refactor
Reduce duplication & add clarity in Ab.spec
Make DOM context available to ab.run()
Add context argument to the AB testing guide
Better DOM context spec wording
Typo
Merge pull request #1222 from guardian/ab-test-segmentation-refactor

Ab test segmentation refactor