allow interacting with IAccountPropertyCollections

- in fact the API could be done in a nicer way and it might be possible to
  work without IAccountPropertyCollection, but only with the
  IAccountProperties.
- To keep it simple at first and not overengineer the blunt attempt is
  followed
- If necessary helpful in the further cause of development adjustements or
  extensions can be done quickly with this base


Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>