Add running a charity specialist sector

Part of https://www.pivotaltracker.com/story/show/67287568
Counterpart to https://github.com/alphagov/panopticon/pull/148
Merge pull request #549 from alphagov/add-running-a-charity-specialist-sector

Add running a charity specialist sector
Add Competition SpecialistSector

Part of https://www.pivotaltracker.com/story/show/67991848 and counterpart
to https://github.com/alphagov/panopticon/pull/147
Merge pull request #548 from alphagov/add-competition-specialist-sector

Add Competition SpecialistSector
Bump gds-api-adapters to 10.5.0

This provides access to the rummager unified search API.
Add new unified search controller

This is used only when the "ui=unified" query parameter is supplied to
search.
Enable position tracking in unified search results
Adding a test for the unified search result page

Also removing an unused instance var in the controller action and fixing
an issue with the tests expecting query params to be extracted with a
symbol.

Relates to https://www.pivotaltracker.com/story/show/65973218