The new Stream administrator role is allowed to manage a stream they
administer, including:
* Setting properties like name, description, privacy and post-policy.
* Removing subscribers
* Deactivating the stream
The access_stream_for_delete_or_update is modified and is used only
to get objects from database and further checks for administrative
rights is done by check_stream_access_for_delete_or_update.
We have also added a new exception class StreamAdministratorRequired.