Add "Users actively browsing licensing pages now"

@abersager
@pbadenski
Interpolate realtime visitors number periodically between refreshes

@pbadenski
@abersager
Applied changes after code review

@robyoung
@pbadenski
Update copy
Merge pull request #93 from alphagov/realtime-visitors-for-licensing

Realtime visitors for licensing
merge master into create-fco-conversion-funnels