Add CRUD operations for Programming Groups

* Correct sorting in table
* Modify page when nested in exercises
* Fix links between pages
* Link from statistics page to programming_groups/index
* Link from submission page to programming_groups/<id>
* Allow filtering for exercise ID on ProgrammingGroup#index
* Add search fields for internal and external user id on pg/index

spec/policies/exercise_policy_spec.rb

@@ -7,11 +7,13 @@ RSpec.describe ExercisePolicy do
 
   let(:exercise) { build(:dummy, public: true) }
 
-  permissions :batch_update? do
-    it 'grants access to admins only' do
-      expect(policy).to permit(build(:admin), exercise)
-      %i[external_user teacher].each do |factory_name|
-        expect(policy).not_to permit(create(factory_name), exercise)
+  %i[batch_update? programming_groups_for_exercise?].each do |action|
+    permissions(action) do
+      it 'grants access to admins only' do
+        expect(policy).to permit(build(:admin), exercise)
+        %i[external_user teacher].each do |factory_name|
+          expect(policy).not_to permit(create(factory_name), exercise)
+        end
       end
     end
   end

spec/policies/programming_group_policy_spec.rb

@@ -7,6 +7,17 @@ RSpec.describe ProgrammingGroupPolicy do
 
   let(:programming_group) { build(:programming_group) }
 
+  %i[index? destroy? show? edit? update?].each do |action|
+    permissions(action) do
+      it 'grants access to admins only' do
+        expect(policy).to permit(create(:admin), programming_group)
+        %i[external_user teacher].each do |factory_name|
+          expect(policy).not_to permit(create(factory_name), programming_group)
+        end
+      end
+    end
+  end
+
   %i[new? create?].each do |action|
     permissions(action) do
       it 'grants access to everyone' do