Fix NPE in Binding.getPolicy() is no policy is present

Fixes "java.lang.NullPointerException: Cannot invoke method minus() on
null object"
Add support for WS-RM Policy version 200502

Add support for Web Services Reliable Messaging Policy Assertion (WS-RM
Policy), the version from february 2005. See
http://schemas.xmlsoap.org/ws/2005/02/rm/policy/ for details.
Merge pull request #217 from bjornvester/Feature-WSRM

Add support for WS-ReliableMessage policy assertions