Ensure all service route have permission decorators

We accidentally miss these sometimes. This code adds a test which
inspects the code to automatically check that any function which:
- handles a route
- accepts a service_id

For each function it checks that each of these routes have the
permissions decorator we’d expect.

Most of the introspection/AST code is adapted from here:
https://mvdwoord.github.io/exploration/2017/08/18/ast_explore.html

app/main/views/agreement.py

@@ -23,6 +23,7 @@ def agreement():
 
 @main.route('/services/<uuid:service_id>/agreement')
 @login_required
+@user_has_permissions('manage_service')
 def service_agreement(service_id):
     return render_template(
         'views/agreement/service-{}.html'.format(current_service.organisation.as_jinja_template),
@@ -41,6 +42,7 @@ def service_download_agreement(service_id):
 
 @main.route('/services/<uuid:service_id>/agreement/accept', methods=['GET', 'POST'])
 @login_required
+@user_has_permissions('manage_service')
 def service_accept_agreement(service_id):
 
     if not current_service.organisation:
@@ -64,6 +66,7 @@ def service_accept_agreement(service_id):
 
 @main.route('/services/<uuid:service_id>/agreement/confirm', methods=['GET', 'POST'])
 @login_required
+@user_has_permissions('manage_service')
 def service_confirm_agreement(service_id):
 
     if (