RCMCardDAV v4.2.1

• Updated French translation (#355)
• Updated German translation
• Fix: Display error message when the sync fails (instead of showing a success message with a duration of -1 seconds)
• Fix: Display error message when a card cannot be updated because it changed on the server since the last sync.
• Fix #356: Don't create group vcards with duplicate members, don't fail to process them if we receive one from the
  server
• New: Action in the preferences to clear the local cache of an addressbook, to allow a full sync from scratch. This is
  meant to fix errors in the local state that cannot be repaired from incremental syncs, as might be the result of issue
  #356.