Accessibility fixes and refactoring

- fix missing content within the form h1
- remove duplication between the form legend and caption
- better semantics for search result
- add hidden h2s to the index to aid screenreaders
- add 'results-list' class to all the results lists on the page
- remove markup bloat from 'no results' page
- remove markup bloat from 'so search term' page
Copy fix for hidden H3 at end of results

- changed from "No more results *search term*" to "No more results for
*search term*"
Merge branch 'master' into search-accessibility-fixes

Conflicts:
	app/views/search/_form.html.erb
	app/views/search/_result.html.erb
	app/views/search/index.html.erb
change test selector to match new HTML

- have introduced H3s so the class of .search-result-title is no longer
used
Remove redundant tests

We've removed the total result count from the page, so these tests are
no longer needed
Render results only if there is a search term.
Modify tests relating to changed microcopy
Modify tests to reflect new .meta HTML
Consistent use of search_term.present
Merge pull request #332 from alphagov/search-accessibility-fixes

Search accessibility fixes