* Add MarketBoard service and associated interfaces, test and data widget
* Dispose of events properly
* Make listings readonly lists + provide internal list for internal use
* Rename CatalogId to ItemId on interfaces, have kept CatalogId internally as it's technically correct
* Removed RetainerOwnerId from the public interface
* Removed NextCatalogId from the public interface
* Updated test text
* Null events in scoped service disposal
