Improve registrar area linked user switch

- Introduce profile
- Move linked users to profile
- Use PUT

#599

spec/presenters/user_presenter_spec.rb

@@ -0,0 +1,16 @@
+require 'rails_helper'
+
+RSpec.describe UserPresenter do
+  let(:presenter) { described_class.new(user: user, view: view) }
+
+  describe '#login_with_role' do
+    let(:user) { instance_double(ApiUser,
+                                 login: 'login',
+                                 roles: %w[role],
+                                 registrar_name: 'registrar') }
+
+    it 'returns username with role and registrar' do
+      expect(presenter.login_with_role).to eq('login (role) - registrar')
+    end
+  end
+end