SLING-3401 Support multiple bundles for the jarWebSupport

The solution is to extend the ArtifactDefinition to internally support
a collection of ArtifactDefinitions named "bundles". 

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1570154 13f79535-47bb-0310-9956-ffa450edef68