Don't show result tabs when only top results

The exception being when there is a government organisation filter: we want to
show the tabs because you might have filtered it such that there are no results,
but you should have a "way out".

This should remove the distraction of the tabs when they won't contain anything.
Merge pull request #378 from alphagov/dont_show_tabs_when_only_top_results

Don't show result tabs when only top results