68355394 store needs in db

    - added api_id column to Organisation model
      because needs api returns organisation_ids with ids of Organisations.
      https://github.com/alphagov/govuk_need_api/blob/master/test/functional/needs_controller_test.rb#L150
      example:
         organisation_ids: ["cabinet-office","department-for-transport"]
    - corrected ImportOrganisations script (added saving of api_id)
    - added ImportNeeds task
    - corrected related associations ContentNeed and ContentPlanNeed
      So, these to tables stored api id of need in need_id
      Now when we store Needs in out db table it should store id of database entry
    - corrected calls to needs in app
    - corrected Rspec tests
    
    Important note:
      1. migration 20140505144311_correct_needs_associations_structure.rb
        is oriented to correct Needs realated associations ContentNeed and ContentPlanNeed.
        So, it's important to have in db already populated Organisations and Needs.
        So, API_CLIENT_CREDENTIALS should not be empty if you are running it on staging or prod envs.
        If you run it in dev env - you can uncomment line 15:
          # PopulateOrganisationAndNeedForDevEnv.run
        This will populate test Organisation and Needs.
    
      2. In case if you already run rake db:migrate, but needs db table was empty
         - you can then run:
           rake db:import to import needs from API or
           rake db:populate_organisation_and_need_for_dev_env if you have no access to API
         - and the run:
           rake db:correct_need_associations - it will correct ContentPlanNeed and ContentNeed tables