WIP: Rebuild event registration form in vue

...s/apps/paweljong/frontend/components/event/events.graphql

...nents/event_additional_field/eventAdditionalFieldMixin.js

...d/components/event_registration/EventRegistrationForm.vue

...ents/event_registration/eventRegistrationMutation.graphql

...ng/frontend/components/event_registration/helpers.graphql

aleksis/apps/paweljong/frontend/index.js

aleksis/apps/paweljong/frontend/messages/en.json

aleksis/apps/paweljong/schema/__init__.py

aleksis/apps/paweljong/schema/checkpoint.py

aleksis/apps/paweljong/schema/event.py

aleksis/apps/paweljong/schema/event_additional_field.py

aleksis/apps/paweljong/schema/event_registration.py

aleksis/apps/paweljong/schema/terms.py