Always return active filters in facets

Also, always return active filters first in facets.  eg, if a filter is
applied for organisation "HMRC", the facet value for the organisation
field will always contain "HMRC" first.

It's possible in various ways for the search UI to have filters which
are applied but whose values are not represented in the results of the
query.  This change makes these filters come back in the facet values,
so that they get displayed in the UI and can be removed by the user.

Fixes https://www.pivotaltracker.com/story/show/69915644
Refactor the presented_facets method

Was getting very cluttered; split it into several component parts.
Whitespace.
Merge pull request #228 from alphagov/always_return_active_filters_in_facets

Always return active filters in facets

https://www.pivotaltracker.com/story/show/69915644
Correct schema for best bets

We'd named the stemmed query field stem_query, but search-admin is
emitting stemmed_query.  It doesn't really matter which is used, so
switch rummager's config.
Merge pull request #229 from alphagov/correct_best_bet_schema

Correct schema for best bets
Remove combined search endpoints.
Merge pull request #230 from alphagov/remove-combined-search-endpoints

Remove combined search endpoints.
Always add popularity to content indexes

Check if the index is an "auxilary" index, and if not add the popularity
field.  We don't just check if the index is a "content" index, because
many of the tests make indexes which are neither content or auxilary
indexes (eg, "rummager_test"), and these should have popularity values
added.

Previously, we were only adding popularity fields to indexes when a
popularity value was found matching the value of the "link" field.  This
meant that most of our tests were producing documents without a
popularity value.  It turns out that elasticsearch 0.90 is more fussy
about the popularity field existing when used in a script than 0.20, and
as such VMs running 0.90.12 fail their integration tests.

This probably doesn't affect production.  It could if:
 - the page-traffic index went missing on production
 - an index migration was performed
 - no documents contained a popularity value
Merge pull request #231 from alphagov/always_set_popularity

Always add popularity to content indexes
Remove New Relic integration.

We never ended up using this beyond preview.
Merge pull request #232 from alphagov/remove-newrelic

Remove New Relic integration
Whitespace.
Provide metasearch (best_bets) mappings for tests.

Removes unused `elasticsearch_schema.fixture.yml`.
Add debugger for integration tests.
Pass type to search to Index.raw_search

Allow the document type to be passed to raw_search, so that we can just
search for, say, documents of type best_bet.
Add metasearch_index_name to the config
Add BestBetsChecker to look up best bets

This fetches best bets from the metasearch index, and merges multiple
best bets appropriately.
Tell test helper about metasearch helper
Raise a clearer error for invalid index names