Have the ID of Trust in toString():
- It is typically used for searching logs. Therefore the ID is useful for searching.
- Remove the nickname and the truster/trustee ID: The truster/trustee ID is contained in the ID. The nickname can change from null to something else so it is a good idea to prevent people from searching for trusts by nickname@ID by removing it.
Delete the client if it doesn't have any more subscriptions.
Fix class-level JavaDoc of SubscriptionManager to be consistent with the introduction of the "Client" class:
- Also remove FIXME which has already been resolved
- The remaining JavaDoc of SubscriptionManager is yet to be adapted