Clarify wording on site traffic module.

We had some user feedback that this could be improved.
Tighten up wording on Carer's Allowance dashboard.

Make minor text changes for neater wording on CA dashboard.
Change wording on GOV.UK trending module.

We had some user feedback saying that "increase" should be "percentage
increase" on the trending content list. This is true, so fixed here.

Also changed "greatest" to "largest".

Also make changes in no-realistic-dashboard, just for neatness.
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Merge pull request #250 from alphagov/bugfix/minor-wording-changes

Minor wording changes on GOV.UK and CA dashboards