Rename additional/custom event to personal event

...is/core/frontend/components/calendar/CalendarOverview.vue

...omponents/calendar/personal_event/PersonalEventDialog.vue

.../components/calendar/personal_event/personalEvent.graphql

...end/components/calendar_feeds/details/PersonalDetails.vue

aleksis/core/frontend/messages/de.json

aleksis/core/frontend/messages/en.json

.../core/migrations/0056_rename_customevent_personalevent.py

aleksis/core/models.py

aleksis/core/preferences.py

aleksis/core/rules.py

aleksis/core/schema/__init__.py

aleksis/core/schema/personal_event.py

aleksis/core/util/predicates.py