CamelIMAPXExtdStore: metadata handling for folder create/store
CamelIMAPXExtdStore: metadata handling for folder create/store

* when creating a new folder, no need to do more than
  what our parent does - CamelKolabIMAPXStore, which uses
  us, will take care of setting folder metadata
* when deleting a folder, we drop the metadata for that
  folder from our in-mem cache (hash table) so we do not
  accidentally return wrong annotation data in the event
  of a folder of the same name being created later on

GNOME/evolution-kolab,GNOME/evolution-kolab