Fix complaints counter, the destroy option and statistics

app/assets/javascripts/management.js

app/assets/javascripts/management/complaints.js

app/controllers/management/complaints_controller.rb

app/controllers/management/statistics_controller.rb

app/views/management/complaints/index.html.erb

app/views/management/statistics/complaints.html.erb

app/views/management/statistics/learning_objects.html.erb

app/views/shared/management/_nav_menu.html.erb

config/routes.rb