zb: Make Connection fields private

The following discussion from !60 (merged) should be addressed:

• @zeenix started a discussion:

  Hmm.. we should make these fields private and provide getters. From user's POV unique_name must always be correctly set after Connection is created.

done for Connection, but I bet there are more to cover while working on the doc. Closing this for now.

closed

mentioned in commit 37948281