proton::connection objects (and others too) don't have useful names

[Issue "reimagined" to fit the actual use case.]
If you want to report to the user and refer to a connection (and probably other proton objects) there is no easy way to get a unique name that we can use to refer to a connection.

The name is distinct from the url used to create the connection (although url would work as a name). The name is also distinct from a printable representation of the object.

Originally the issue was:
Although the user could just remember whatever url they used to create a given connection, it is duplicative when the library has the info around.

Also if it is not provided then the user has to plumb to info to places it is needed inside the event handlers, however the handlers will already get the connection context object anyway so that is unecessary and an extra burden.