Exposing AMQP filter set for Source terminus

[ppatierno]

The getSource() and getTarget() methods in the ProtonLinkImpl class returns simple Source and Target interfaces with few info from the org.apache.qpid.proton.amqp.transport package.
The real instances used are Source and Target classes from org.apache.qpid.proton.amqp.messaging and in order to use them with Vert.x Proton, an explicit cast is needed.

[ppatierno]

The problem seems to be related to the underlying Proton library used.
A JIRA is already opened for that :

https://issues.apache.org/jira/browse/PROTON-1177