rename Whitehall.government_search_index_name to Whitehall.government_search_index_url
rename *search_index_name method for detailed and maintream

to detailed_guidance_search_index_url and mainstream_search_index_url
for consistancy
DocumentSearch to use Whitehall.government_search_index_name
remove only_published filter

we only index publiushed documents now
We only search published documents so rename methods