Setting last successful message receive during catch up

[brandonhilkert]

During catch up, messages are processed through the normal channel where last successful process timestamp is set based on Time.now. However, items from the catch up list are historic and have a score (time) associated with them.

It would make sense to set that timestamp based on the historic message and its own score (timestamp) so that if for some reason the system crashes during catch up, it'll process messages starting from the place it shit the bed.