Before starting working on adding dictionaries we should:

• Move all collection internal classes (e.g.UnmanagedRealmSet, ManagedRealmList, etc.) to separate files
• Align to a reasonable extent the test framework of both lists and sets and consider dictionaries while at it, though it might not be fully possible due to maps not being {{Collection}}s.
• Align to a reasonable extent the test framework of collection notifications.
• Optimise the notification callback code in realm_api_helpers - see comments in register_notification_cb.
• More?