Add tests to OffencesController

[colinbruce]

Something like

  let(:params) { { fee_scheme: 'fee_reform', description: 'Offence 1', band_id: 1, category_id: 1, format: :json} }

  it do
    should permit(:fee_scheme, :description, :search_offence, :category_id, :band_id).for(:index, params: params, verb: :get)
  end

But this introduces more Deprecation warnings due to shoulda matchers see closed PR chain

Updating Gemfile to use shoulda-matchers master branch then breaks association tests e.g.

  1) Fee::FixedFee should belong to fee_type optional: true
     Failure/Error: it { should belong_to(:fee_type) }
       Expected Fee::FixedFee to have a belongs_to association called fee_type (the association should have been defined with `optional: true`, but was not)