Add submission url to submission's json view

Author: Redande

app/controllers/api/v8/core/submissions_controller.rb

@@ -67,6 +67,7 @@ def show
               points: @submission.points_list,
               validations: @submission.validations,
               valgrind: @submission.valgrind,
+              submission_url: submission_url(@submission),
               solution_url: @exercise.solution.visible_to?(current_user) ? view_context.exercise_solution_url(@exercise) : nil,
               submitted_at: @submission.created_at,
               processing_time: @submission.processing_time,