Ab test for number of items to initially show in news container

If in test, effectively displays as if the 'show more' button was pressed once

Hypothesis
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Click through of stories that would have been hidden will increase (compared to when they are hidden)

Plus this will have no (or comparatively no) negative effect on click through to articles further down

Also moved over related js files to use the new smaller common modules (`utils/mediator`, `$`, etc)