Support batch.xml in Batch project model

Default loading of batch artifacts described by JSR-352 is provided by batch.xml:

<batch-artifacts xmlns="http://xmlns.jcp.org/xml/ns/javaee">
<ref id="<reference-name>" class="<impl-class-name>" />
</batch-artifacts>

Batch implementations may define specific loaders and probably most popular is going to be the use of javax.inject.Named annotation.
For the completeness, we have better to support the default way as well.