Add 'acronym' to the government schema

This lets us submit and extract the 'acronym' for Organisations (though there's
nothing stopping anything else using it).

When we're using the field from the index, we can remove the code that fills it
in by processing the title.
Index acronyms and boost them just as we do titles

This is to ensure that organisations continue to rank brilliantly for their
acronym.

Thanks to @fatbusinessman
Merge pull request #125 from alphagov/add_acronym_to_government_schema

Add 'acronym' to the government schema
Fix broken test

Broken by:
146515674f8df71fdd6949371c0f2a4062d331fd

Adding an extra boosted field meant that the condition the test is looking for
was no longer the fourth element in the array. Instead, let's look for it in a
semantic way.

There's also an extra field in the shingle condition, so add that too.