BATCH-2227: Allow multiple configs (xmls, java-files, packages) to be loaded in ApplicationContextFactory

With the ApplicationContextFactory it is not possible to load a Job context from multiple resources. 

At the moment you can only give one Resource (i.e. XML file) to the GenericApplicationContextFactory constructor to load beans from it. With this, it is not possible to use a separate XML file for abstract behaviour (abstract steps and jobs) without importing it explicitly into the job XML. I have the usecase, that I want do add abstract job and step definitions globally and I don't want to force any Job XML provider to import it.

I found that the GenericXmlApplicationContext that is used inside the GenericApplicationContextFactory is already able to load from multiple resources. So I extended the AbstractApplicationContextFactory and GenericApplicationContextFactory, that an array of resources is allowed to be put into the constructor of GenericApplicationContextFactory.

With the use of Var-Args the new implementation is backward compatible with the old one as Java just creates an one-element-array if you put only one resource into the constructor.

What do you think about it?