Rewrite copied events: suffix, extra fields, templates

Released 11 October as Custom text and rules. Pick Custom on a copy's title, description or location and write your own text, using pieces of the original (its title, description, location or the calendar name). That covers a suffix instead of a prefix, sending a venue held in the description to the location, and labelling each copy with its source calendar. Plus and above can add "if this, then that, otherwise" rules to title, description, location, privacy and free or busy, with a live preview before saving.

Not part of this release: adding a fixed invitee to the copy and carrying the source calendar's colour onto copies.