akonadi-contacts links to contact-editor, so add to find_dependency

Otherwise, find_package for AkonadiContact says:
  [...] but it set KF5AkonadiContact_FOUND to FALSE so package "KF5AkonadiContact"
  is considered to be NOT FOUND.  Reason given by package:

  The following imported targets are referenced, but are missing:
  KF5::ContactEditor