Add a filter to exclude specialist_sector documents

This modifies UnifiedSearchBuilder, adding a new filter to all search 
queries that excludes documents in the specialist_sector format.
Include the sectors filter in test query_options

This is a first pass at trying to fix tests broken by the inclusion of
the new filter, by including the specialist sectors filter in the 
default query used by most tests when building stubs.
Fix UnifiedSearcherTest
Fix UnifiedSearchBuilderTest
Merge pull request #253 from alphagov/register-specialist-sectors-in-rummager

Exclude specialist sector documents from unified search results
Remove stemming override for 'permitting'

Environment Agency prefer ‘environmental permit’ and ‘environmental
permitting’ to be interchangeable
Make delete path work when queueing enabled

The delete action takes an optional `_type` parameter, but the queueing
enabled branch of the action hadn't been updated to use it.
Make DeleteWorker#perform backwards compatible
Merge pull request #255 from alphagov/fix-queued-delete

Make delete path work when queueing enabled
Synonym updates following unified search and best bets

Remove synonyms that are no longer needed with recent weighting
improvements or can now be handled better through best bets; also
reinstate a couple that were causing problems in the past
Merge pull request #256 from alphagov/synonyms-20140714

Synonym updates following unified search and best bets
Analyze the specialist_sectors field

We were originally not analyzing the specialist_sectors field because we
had a plan to move to storing this in an internal tags field.  However,
we don't currently have any searches which require a single internal
tags field, so this is probably a misstep for now.  Changing the field
to be analyzed will make it available for searches after we next run a
deploy:migrations.

Also, don't allow use of the tags field in searches, since it shouldn't
be visible externally.
Expand specialist_sectors field

The specialist sectors aren't yet being indexed, but when they are this
will the specialist_sectors field in search results.

The main reason for implementing this now is that we also want to store
example values in the SpecialistSectorsRegistry, so we need to create
that object first.
Functional test for sector expansion
Support stubbing the metasearch index

Also, memoize the index stubs so that repeated calls to them within a
test return the same stub.
Allow extra options to be supplied for faceting

We want to allow callers to request that a set of example documents are
returned when faceting.  As a first step towards this, this commit
changes the facet parameters to accept a set of additional
comma-separated facet parameters; within each facet parameter, keys and
values are separated by colons.  For example:

    facet_organisations=10,examples:5,example_fields:link:title,example_scope:global

The parameters will actually be used by subsequent commits.
Add Index.msearch method for multiple searches

This accesses the _msearch endpoint in Elasticsearch to allow lots of
queries to be run concurrently.  Useful for doing lots of individual
lookups.
Replace unused iteration parameter name with _
WIP