PROTON-382: Added properties field to the Perl Message class.

Added the set_property and get_property methods to assign and fetch
individual values. Added unit test for validating the APIs.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1520389 13f79535-47bb-0310-9956-ffa450edef68