Create feature for jbpm-workitems bundle

In the drools karaf features there is no feature for the jbpm-workitems bundle:

https://github.com/droolsjbpm/droolsjbpm-integration/blob/master/drools-osgi/drools-karaf-features/src/main/filtered-resources/repository/features.xml#L116

It would be good to add a feature with this bundle used in the fuse-bxms-integ repository to avoid specify a version, and have the possibility to include a range of versions, as we do for other drools bundles used in the fuse-integ-repository. Take a look:

https://github.com/jboss-integration/fuse-bxms-integ/blob/master/karaf/karaf-features/src/main/resources/features.xml#L41