PROTON-693: Implement C-API wrappers in Java for jython, clean up Url implementation.

- Java implementation of fake C API for Jython SWIG wrappers based on messenger.impl.Address.
- Minor extensions to Address.java
- Minor change to Address.java to be consistent with C parser on one corner case:
  - is url("/foo") a host called "/foo" or an empty host and a path "foo"
  - fixed Java parser to agree with C - path "foo"
- Rename getters from url_* to url_get_*.
- Use pn_string_t formatting functions to build URL string.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627086 13f79535-47bb-0310-9956-ffa450edef68