Rewrite copied events: suffix, extra fields, templates

More control over how a copied event reads. First steps: a suffix instead of a prefix on the title, appending a field (such as a venue held in the description) to the location, adding a fixed invitee to the copy, carrying the source calendar's colour onto copies, and marking individual events private. Later: templates with placeholders for title, description and location, and simple if-this-then-that rules.