Add a duplicate function to invitations and booking pages.

User Story:

We create often multiple corresponding invitations which will carry the same slots and other preferences. It is very cumbersome currently to create multiple but similar invitations. I want to copy the preferences and slots from one invitation over to another.

Suggestion

Create a duplicate function. By this after duplicating one would just change some of the properties of the new invitation, for instance often only the title. But it would prevent, that you have re-select the same slots and properties over and over.