Include Organisation acronym in search index

This lets us remove some ugliness in Rummager that pulls the acronym out from
the title.

I've left the acronym in the title for fear that removing it will harm the
ranking of organisation pages for the organisation acronyms, and then force us
to add acronyms for every organisation...
Exclude acronyms for organisation titles in search

Now that they are indexed separately, it can become a view concern whether we
include the acronym in the result title.
Add a data migration to reindex Organisations

Now that we exclude acronym from the title and include it separately, we should
update the index.

The changes in Rummager need to be deployed and applied first for it to work as
intended.
Merge pull request #656 from alphagov/include_organisation_acronyms_in_search_index

Include Organisation acronym in search index