Merge branch 'develop' into 'master'

Gemfile

Gemfile.lock

app/controllers/concerns/paginator.rb

app/controllers/v1/complaint_votes_controller.rb

app/controllers/v1/complaints_controller.rb

app/controllers/v1/contacts_controller.rb

app/controllers/v1/learning_objects_complaints_controller.rb

app/controllers/v1/sessions_controller.rb

app/controllers/v1/submissions_controller.rb

app/controllers/v1/unlocked_achievements_controller.rb

app/controllers/v1/users_controller.rb

app/mailers/application_mailer.rb

app/mailers/contacts_mailer.rb

app/mailers/user_mailer.rb

app/models/achievement.rb

app/models/action.rb

app/models/action_counter.rb

app/models/collection.rb

app/models/collection_item.rb

app/models/complaint.rb