ContextJXPathBindingBuilder provides a helper class for the Factory
implemented in JXPathBindingManager that helps construct the
actual ContextJXPathBinding out of the configuration in the
provided configElement which looks like:
<wb:context path="xpath expression">
<!-- in here come the nested child bindings on the sub-context -->
</wb:context>
buildBinding(Element bindingElm,
JXPathBindingManager.Assistant assistant)
Creates an instance of ContextJXPathBinding with the configured
path and nested child bindings from the declarations in the bindingElm