Organisations now have their acronyms indexed

They are no longer included in the title and are indexed separately. See:
https://github.com/alphagov/rummager/commit/97d354eab40031c8d0ad3a36b4b27fdb973f48b4
https://github.com/alphagov/whitehall/commit/901e552e87b16adf14dfa8d056c8c16e6ab44827
https://github.com/alphagov/whitehall/commit/428366cf7295568f2363342a5d33016f57422058
Merge remote-tracking branch 'origin/dont_fill_in_missing_org_acronyms'

Conflicts:
	test/unit/organisation_registry_test.rb - test deleted in branch was
also modified to include a slug field